diff --git a/backend/app/main.py b/backend/app/main.py
index 52156e5..d2064c3 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -1,6 +1,7 @@
 from fastapi import FastAPI, Depends, HTTPException, APIRouter, status, Response
 from fastapi.middleware.cors import CORSMiddleware
 from sqlalchemy.orm import Session
+from sqlalchemy import func
 from typing import List, Optional, Dict, Any
 from datetime import datetime, timedelta, date
 import math
@@ -263,6 +264,34 @@ class DrugWithVariantsResponse(BaseModel):
     class Config:
         from_attributes = True
 
+
+class VariantSummaryResponse(BaseModel):
+    """Lightweight variant summary returned by GET /drugs list — no packs or batches."""
+    id: int
+    drug_id: int
+    strength: str
+    quantity: float
+    unit: str
+    low_stock_threshold: float
+    has_inventory_history: bool = False
+    expired_quantity: float = 0.0
+
+    class Config:
+        from_attributes = True
+
+
+class DrugSummaryResponse(BaseModel):
+    """Lightweight drug summary for the main list — variants without packs or batches."""
+    id: int
+    name: str
+    description: Optional[str] = None
+    is_controlled: bool = False
+    locations: List[str] = []
+    variants: List[VariantSummaryResponse] = []
+
+    class Config:
+        from_attributes = True
+
 class DispensingAllocationCreate(BaseModel):
     batch_id: int
     quantity: float
@@ -399,6 +428,40 @@ def enrich_variant_with_batches(db: Session, variant: DrugVariant) -> Dict[str,
     return variant_dict
 
 
+def serialize_variant_with_packs(db: Session, variant: DrugVariant) -> Dict[str, Any]:
+    """Return variant data with packs but without batch details (level-2 detail)."""
+    has_batch_history = (
+        db.query(Batch.id)
+        .filter(Batch.drug_variant_id == variant.id)
+        .first()
+        is not None
+    )
+    has_dispense_history = (
+        db.query(Dispensing.id)
+        .filter(Dispensing.drug_variant_id == variant.id)
+        .first()
+        is not None
+    )
+    packs = (
+        db.query(VariantPack)
+        .filter(VariantPack.drug_variant_id == variant.id)
+        .order_by(VariantPack.is_active.desc(), VariantPack.id.asc())
+        .all()
+    )
+    return {
+        "id": variant.id,
+        "drug_id": variant.drug_id,
+        "strength": variant.strength,
+        "quantity": variant.quantity,
+        "unit": variant.unit,
+        "base_unit": variant.unit,
+        "low_stock_threshold": variant.low_stock_threshold,
+        "has_inventory_history": has_batch_history or has_dispense_history,
+        "packs": [serialize_variant_pack(pack) for pack in packs],
+        "batches": [],
+    }
+
+
 def serialize_batch_response(db: Session, batch: Batch) -> Dict[str, Any]:
     location = db.query(Location).filter(Location.id == batch.location_id).first()
     pack = None
@@ -866,21 +929,112 @@ def admin_change_password(user_id: int, password_data: AdminPasswordChange, db:
 def read_root():
     return {"message": "Drug Inventory API"}
 
-@router.get("/drugs", response_model=List[DrugWithVariantsResponse])
+@router.get("/drugs", response_model=List[DrugSummaryResponse])
 def list_drugs(db: Session = Depends(get_db), current_user: User = Depends(get_current_user)):
-    """Get all drugs with their variants"""
+    """Get all drugs with lightweight variant summaries (no packs or batches)."""
     drugs = db.query(Drug).all()
+    if not drugs:
+        return []
+
+    drug_ids = [d.id for d in drugs]
+
+    all_variants = (
+        db.query(DrugVariant)
+        .filter(DrugVariant.drug_id.in_(drug_ids))
+        .all()
+    )
+    variants_by_drug: Dict[int, list] = {}
+    for v in all_variants:
+        variants_by_drug.setdefault(v.drug_id, []).append(v)
+
+    variant_ids = [v.id for v in all_variants]
+    if not variant_ids:
+        return [
+            {
+                "id": d.id,
+                "name": d.name,
+                "description": d.description,
+                "is_controlled": bool(d.is_controlled),
+                "locations": [],
+                "variants": [],
+            }
+            for d in drugs
+        ]
+
+    # Variant IDs that have ever had a batch received
+    batch_history_ids = set(
+        row[0]
+        for row in db.query(Batch.drug_variant_id)
+        .filter(Batch.drug_variant_id.in_(variant_ids))
+        .distinct()
+        .all()
+    )
+
+    # Variant IDs that have ever had a dispense
+    dispense_history_ids = set(
+        row[0]
+        for row in db.query(Dispensing.drug_variant_id)
+        .filter(Dispensing.drug_variant_id.in_(variant_ids))
+        .distinct()
+        .all()
+    )
+
+    # Sum of expired active batch stock per variant
+    today = date.today()
+    expired_rows = (
+        db.query(Batch.drug_variant_id, func.sum(Batch.quantity))
+        .filter(
+            Batch.drug_variant_id.in_(variant_ids),
+            Batch.quantity > 0,
+            Batch.expiry_date < today,
+        )
+        .group_by(Batch.drug_variant_id)
+        .all()
+    )
+    expired_by_variant: Dict[int, float] = {row[0]: float(row[1]) for row in expired_rows}
+
+    # Distinct location names per drug (from active batch stock)
+    location_rows = (
+        db.query(DrugVariant.drug_id, Location.name)
+        .join(Batch, Batch.drug_variant_id == DrugVariant.id)
+        .join(Location, Location.id == Batch.location_id)
+        .filter(
+            DrugVariant.drug_id.in_(drug_ids),
+            Batch.quantity > 0,
+        )
+        .distinct()
+        .all()
+    )
+    locations_by_drug: Dict[int, list] = {}
+    for drug_id, loc_name in location_rows:
+        locations_by_drug.setdefault(drug_id, []).append(loc_name)
+
     result = []
     for drug in drugs:
-        variants = db.query(DrugVariant).filter(DrugVariant.drug_id == drug.id).all()
-        drug_dict = {
-            "id": drug.id,
-            "name": drug.name,
-            "description": drug.description,
-            "is_controlled": bool(drug.is_controlled),
-            "variants": [enrich_variant_with_batches(db, v) for v in variants],
-        }
-        result.append(drug_dict)
+        drug_variants = variants_by_drug.get(drug.id, [])
+        variant_summaries = [
+            {
+                "id": v.id,
+                "drug_id": v.drug_id,
+                "strength": v.strength,
+                "quantity": v.quantity,
+                "unit": v.unit,
+                "low_stock_threshold": v.low_stock_threshold,
+                "has_inventory_history": v.id in batch_history_ids or v.id in dispense_history_ids,
+                "expired_quantity": expired_by_variant.get(v.id, 0.0),
+            }
+            for v in drug_variants
+        ]
+        result.append(
+            {
+                "id": drug.id,
+                "name": drug.name,
+                "description": drug.description,
+                "is_controlled": bool(drug.is_controlled),
+                "locations": locations_by_drug.get(drug.id, []),
+                "variants": variant_summaries,
+            }
+        )
     return result
 
 @router.get("/drugs/low-stock", response_model=List[DrugWithVariantsResponse])
@@ -910,18 +1064,18 @@ def low_stock_drugs(db: Session = Depends(get_db), current_user: User = Depends(
 
 @router.get("/drugs/{drug_id}", response_model=DrugWithVariantsResponse)
 def get_drug(drug_id: int, db: Session = Depends(get_db), current_user: User = Depends(get_current_user)):
-    """Get a specific drug with its variants"""
+    """Get a specific drug with its variants and packs (no batch detail — level-2 detail)."""
     drug = db.query(Drug).filter(Drug.id == drug_id).first()
     if not drug:
         raise HTTPException(status_code=404, detail="Drug not found")
-    
+
     variants = db.query(DrugVariant).filter(DrugVariant.drug_id == drug.id).all()
     drug_dict = {
         "id": drug.id,
         "name": drug.name,
         "description": drug.description,
         "is_controlled": bool(drug.is_controlled),
-        "variants": [enrich_variant_with_batches(db, v) for v in variants],
+        "variants": [serialize_variant_with_packs(db, v) for v in variants],
     }
     return drug_dict
 
diff --git a/frontend/app.js b/frontend/app.js
index 27e25cb..3227e9c 100644
--- a/frontend/app.js
+++ b/frontend/app.js
@@ -1,5 +1,7 @@
 const API_URL = '/api';
-let allDrugs = [];
+let allDrugs = []; // level-1 summaries: no packs, no batches
+let loadedDrugDetails = new Map(); // drugId → full drug with variant packs (level-2)
+let loadedVariantBatches = new Map(); // variantId → Batch[] (level-3)
 let currentDrug = null;
 let showLowStockOnly = false;
 let selectedLocationFilter = '';
@@ -450,9 +452,21 @@ function setupEventListeners() {
     });
     
     // User menu
-    if (userMenuBtn) userMenuBtn.addEventListener('click', () => {
+    if (userMenuBtn) userMenuBtn.addEventListener('click', (e) => {
+        e.stopPropagation();
         const dropdown = document.getElementById('userDropdown');
-        if (dropdown) dropdown.style.display = dropdown.style.display === 'none' ? 'block' : 'none';
+        if (dropdown) {
+            const isHidden = getComputedStyle(dropdown).display === 'none';
+            dropdown.style.display = isHidden ? 'block' : 'none';
+        }
+    });
+
+    document.addEventListener('click', (e) => {
+        const dropdown = document.getElementById('userDropdown');
+        const btn = document.getElementById('userMenuBtn');
+        if (dropdown && btn && !btn.contains(e.target) && !dropdown.contains(e.target)) {
+            dropdown.style.display = 'none';
+        }
     });
     
     if (changePasswordBtn) changePasswordBtn.addEventListener('click', openChangePasswordModal);
@@ -532,22 +546,24 @@ async function loadDrugs() {
                 const newVariant = drug?.variants?.find(v => !restore._existingVariantIds.has(v.id));
                 if (newVariant) {
                     restore.variantId = newVariant.id;
-                    // If no pack snapshot, all packs are new — pick the first active one
+                    // If no pack snapshot, all packs are new — pick the first active one from detail
                     if (!restore._existingPackIds) {
-                        const firstPack = getActivePacksForVariant(newVariant)?.[0];
+                        await ensureDrugDetailLoaded(restore.drugId);
+                        const detailVariant = getVariantById(newVariant.id);
+                        const firstPack = getActivePacksForVariant(detailVariant)?.[0];
                         if (firstPack) restore.packId = firstPack.id;
                     }
                 }
             }
-            // Resolve new pack by diffing (add-pack flow)
+            // Resolve new pack by diffing (add-pack flow) — need packs from loaded detail
             if (restore._existingPackIds && restore.drugId && restore.variantId) {
-                const drug = allDrugs.find(d => d.id === restore.drugId);
-                const variant = drug?.variants?.find(v => v.id === restore.variantId);
+                await ensureDrugDetailLoaded(restore.drugId);
+                const variant = getVariantById(restore.variantId);
                 const newPack = getActivePacksForVariant(variant)?.find(p => !restore._existingPackIds.has(p.id));
                 if (newPack) restore.packId = newPack.id;
             }
 
-            _reinitGtinMappingModal(restore);
+            await _reinitGtinMappingModal(restore);
         }
 
         // After handleAddDrug's loadDrugs fires: find the newly created drug and set up
@@ -959,10 +975,10 @@ function isBatchExpired(batch) {
     return expiryDate < today;
 }
 
-function renderVariantInventoryDetails(variant) {
+function renderVariantInventoryDetails(variant, batches) {
     const activePacks = getActivePacksForVariant(variant);
     const isReadOnly = currentUser?.role === 'readonly';
-    const batches = [...(variant.batches || [])]
+    const sortedBatches = [...(batches || [])]
         .filter(batch => Number(batch.quantity) > 0)
         .sort((a, b) => new Date(a.expiry_date) - new Date(b.expiry_date));
 
@@ -975,8 +991,8 @@ function renderVariantInventoryDetails(variant) {
         `).join('')
         : '<div style="padding: 6px 8px; background: #ffffff; border: 1px dashed #cfd8e3; border-radius: 5px; font-size: 0.9em; color: #6b7280;">No active packs configured</div>';
 
-    const batchesHtml = batches.length > 0
-        ? batches.map(batch => {
+    const batchesHtml = sortedBatches.length > 0
+        ? sortedBatches.map(batch => {
             const locationLabel = getBatchLocationLabel(batch);
             const expired = isBatchExpired(batch);
             const hasPackState = batch.current_full_pack_count != null && batch.current_loose_base_units != null && batch.received_pack_unit_name;
@@ -1067,6 +1083,16 @@ async function handleDisposeBatch(e) {
         if (modal) {
             closeDisposeBatchModal();
         }
+        // Find which variant this batch belongs to and invalidate its batch cache
+        const batchVariantId = (() => {
+            for (const [vid, batches] of loadedVariantBatches) {
+                if (batches.some(b => b.id === batchId)) return vid;
+            }
+            return null;
+        })();
+        if (batchVariantId) {
+            loadedVariantBatches.delete(batchVariantId);
+        }
         await loadDrugs();
         showToast('Expired batch marked as disposed.', 'success');
     } catch (error) {
@@ -1087,13 +1113,7 @@ function updateLocationFilterOptions() {
     const locations = new Set();
 
     allDrugs.forEach(drug => {
-        drug.variants.forEach(variant => {
-            (variant.batches || []).forEach(batch => {
-                if (batch.quantity > 0) {
-                    locations.add(getBatchLocationLabel(batch));
-                }
-            });
-        });
+        (drug.locations || []).forEach(loc => locations.add(loc));
     });
 
     locationFilterSelect.innerHTML = '<option value="">All Locations</option>';
@@ -1388,7 +1408,10 @@ async function updateBatchInfo() {
 
     const variant = getVariantById(variantId);
     if (variant) {
-        populateDispensePackSelect(variant);
+        // Ensure drug detail (with packs) is loaded before populating pack select
+        const drugOfVariant = allDrugs.find(d => (d.variants || []).some(v => v.id === variantId));
+        if (drugOfVariant) await ensureDrugDetailLoaded(drugOfVariant.id);
+        populateDispensePackSelect(getVariantById(variantId));
     }
     updateDispenseModeUi();
     
@@ -1621,14 +1644,10 @@ function renderDrugs() {
         );
     }
 
-    // Apply location filter
+    // Apply location filter using the pre-computed locations list in the summary
     if (selectedLocationFilter) {
         drugsToShow = drugsToShow.filter(drug =>
-            drug.variants.some(variant =>
-                (variant.batches || []).some(batch =>
-                    batch.quantity > 0 && getBatchLocationLabel(batch) === selectedLocationFilter
-                )
-            )
+            (drug.locations || []).includes(selectedLocationFilter)
         );
     }
 
@@ -1650,43 +1669,57 @@ function renderDrugs() {
         const isExpanded = expandedDrugs.has(drug.id);
         const isReadOnly = currentUser.role === 'readonly';
         const isControlled = drug.is_controlled;
-        
-        const variantsHtml = isExpanded ? `
-            ${drug.variants.map(variant => {
-                const variantIsLowStock = variant.quantity <= variant.low_stock_threshold;
-                const variantExpanded = expandedVariants.has(variant.id);
-                const expiredQuantity = (variant.batches || [])
-                    .filter(batch => Number(batch.quantity) > 0 && isBatchExpired(batch))
-                    .reduce((sum, batch) => sum + Number(batch.quantity || 0), 0);
-                const inDateQuantity = Math.max(0, Number(variant.quantity || 0) - expiredQuantity);
-                const quantityDisplay = expiredQuantity > 0
-                    ? `${formatDisplayNumber(inDateQuantity)} ${escapeHtml(variant.unit)} (${formatDisplayNumber(expiredQuantity)} expired)`
-                    : `${formatDisplayNumber(variant.quantity)} ${escapeHtml(variant.unit)}`;
-                return `
-                    <div class="variant-item ${variantIsLowStock ? 'low-stock' : ''}" onclick="toggleVariantExpansion(${variant.id}, event)">
-                        <div class="variant-info">
-                            <div class="variant-details">
-                                <div class="variant-name">${escapeHtml(drug.name)} ${escapeHtml(variant.strength)}</div>
-                                <div class="variant-quantity">${quantityDisplay}</div>
+        const drugDetail = loadedDrugDetails.get(drug.id);
+
+        let variantsHtml = '';
+        if (isExpanded) {
+            if (!drugDetail) {
+                variantsHtml = '<div class="variant-item" style="padding: 12px; color: #6b7280; font-style: italic;">Loading variants…</div>';
+            } else {
+                variantsHtml = drug.variants.map(summaryVariant => {
+                    // Use detail variant (has packs); fall back to summary if not found
+                    const variant = (drugDetail.variants || []).find(v => v.id === summaryVariant.id) || summaryVariant;
+                    const variantIsLowStock = summaryVariant.quantity <= summaryVariant.low_stock_threshold;
+                    const variantExpanded = expandedVariants.has(summaryVariant.id);
+                    // expiredQuantity is pre-computed in the summary
+                    const expiredQuantity = summaryVariant.expired_quantity || 0;
+                    const inDateQuantity = Math.max(0, Number(summaryVariant.quantity || 0) - expiredQuantity);
+                    const quantityDisplay = expiredQuantity > 0
+                        ? `${formatDisplayNumber(inDateQuantity)} ${escapeHtml(summaryVariant.unit)} (${formatDisplayNumber(expiredQuantity)} expired)`
+                        : `${formatDisplayNumber(summaryVariant.quantity)} ${escapeHtml(summaryVariant.unit)}`;
+                    const batches = loadedVariantBatches.get(summaryVariant.id);
+                    const batchesSection = (() => {
+                        if (!variantExpanded) return '';
+                        if (!batches) return '<div style="padding: 10px; color: #6b7280; font-style: italic;">Loading batches…</div>';
+                        return renderVariantInventoryDetails(variant, batches);
+                    })();
+                    return `
+                        <div class="variant-item ${variantIsLowStock ? 'low-stock' : ''}" onclick="toggleVariantExpansion(${summaryVariant.id}, event)">
+                            <div class="variant-info">
+                                <div class="variant-details">
+                                    <div class="variant-name">${escapeHtml(drug.name)} ${escapeHtml(summaryVariant.strength)}</div>
+                                    <div class="variant-quantity">${quantityDisplay}</div>
+                                </div>
+                                <div class="variant-status">
+                                    <span class="variant-badge ${variantIsLowStock ? 'badge-low' : 'badge-normal'}">
+                                        ${variantIsLowStock ? 'Low Stock' : 'OK'}
+                                    </span>
+                                    <span style="margin-left: 8px; font-size: 0.85em; color: #475569;">Inventory ${variantExpanded ? '▼' : '▶'}</span>
+                                </div>
                             </div>
-                            <div class="variant-status">
-                                <span class="variant-badge ${variantIsLowStock ? 'badge-low' : 'badge-normal'}">
-                                    ${variantIsLowStock ? 'Low Stock' : 'OK'}
-                                </span>
-                                <span style="margin-left: 8px; font-size: 0.85em; color: #475569;">Inventory ${variantExpanded ? '▼' : '▶'}</span>
+                            <div class="variant-actions">
+                                ${!isReadOnly ? `
+                                    <button class="btn btn-success btn-small" onclick="event.stopPropagation(); dispenseVariant(${summaryVariant.id})">💊 Dispense</button>
+                                    <button class="btn btn-warning btn-small" onclick="event.stopPropagation(); openEditVariantModal(${summaryVariant.id})">Edit</button>
+                                    <button class="btn btn-danger btn-small" onclick="event.stopPropagation(); deleteVariant(${summaryVariant.id})" title="${summaryVariant.has_inventory_history ? 'Variant has history and cannot be deleted' : ''}">Delete</button>
+                                ` : ''}
                             </div>
+                            ${batchesSection}
                         </div>
-                        <div class="variant-actions">
-                            ${!isReadOnly ? `
-                                <button class="btn btn-success btn-small" onclick="event.stopPropagation(); dispenseVariant(${variant.id})">💊 Dispense</button>
-                                <button class="btn btn-warning btn-small" onclick="event.stopPropagation(); openEditVariantModal(${variant.id})">Edit</button>
-                                <button class="btn btn-danger btn-small" onclick="event.stopPropagation(); deleteVariant(${variant.id})" title="${variant.has_inventory_history ? 'Variant has history and cannot be deleted' : ''}">Delete</button>
-                            ` : ''}
-                        </div>
-                        ${variantExpanded ? renderVariantInventoryDetails(variant) : ''}
-                    </div>
-                `;
-            }).join('')}` : '';
+                    `;
+                }).join('');
+            }
+        }
         
         return `
             <div class="drug-item ${isLowStock ? 'low-stock' : ''} ${isExpanded ? 'expanded' : ''}" onclick="toggleDrugExpansion(${drug.id})">
@@ -1934,6 +1967,7 @@ async function handleDispenseDrug(e) {
         document.getElementById('dispenseForm').reset();
         resetDispensePrintFields();
         closeModal(document.getElementById('dispenseModal'));
+        loadedVariantBatches.delete(variantId); // invalidate level-3 batch cache
         await loadDrugs();
         showToast(successMessage, toastType, toastType === 'warning' ? 5000 : undefined);
     } catch (error) {
@@ -1962,30 +1996,45 @@ function closeEditModal() {
 }
 
 // Show variants for a drug
-function toggleDrugExpansion(drugId) {
+async function toggleDrugExpansion(drugId) {
     if (expandedDrugs.has(drugId)) {
         expandedDrugs.delete(drugId);
         const collapsedDrug = allDrugs.find(drug => drug.id === drugId);
         if (collapsedDrug) {
             (collapsedDrug.variants || []).forEach(variant => expandedVariants.delete(variant.id));
         }
+        renderDrugs();
     } else {
         expandedDrugs.add(drugId);
+        renderDrugs(); // show loading state immediately
+        await ensureDrugDetailLoaded(drugId);
+        renderDrugs();
     }
-    renderDrugs();
 }
 
-function toggleVariantExpansion(variantId, event) {
+async function toggleVariantExpansion(variantId, event) {
     if (event) {
         event.stopPropagation();
     }
 
     if (expandedVariants.has(variantId)) {
         expandedVariants.delete(variantId);
+        renderDrugs();
     } else {
         expandedVariants.add(variantId);
+        if (!loadedVariantBatches.has(variantId)) {
+            renderDrugs(); // show loading state immediately
+            try {
+                const response = await apiCall(`/variants/${variantId}/batches`);
+                if (response.ok) {
+                    loadedVariantBatches.set(variantId, await response.json());
+                }
+            } catch (error) {
+                console.error(`Failed to load batches for variant ${variantId}:`, error);
+            }
+        }
+        renderDrugs();
     }
-    renderDrugs();
 }
 
 // Open add variant modal
@@ -2256,6 +2305,7 @@ async function handleAddVariant(e) {
 
         document.getElementById('variantForm').reset();
         closeModal(document.getElementById('addVariantModal'));
+        loadedDrugDetails.delete(drugId); // invalidate level-2 cache for this drug
         await loadDrugs();
         if (document.getElementById('receiveDeliveryModal')?.classList.contains('show')) {
             refreshDeliveryVariantSelects();
@@ -2369,6 +2419,8 @@ async function handleEditVariant(e) {
         }
 
         closeModal(document.getElementById('editVariantModal'));
+        const variantDrugId = allDrugs.find(d => (d.variants || []).some(v => v.id === variantId))?.id;
+        if (variantDrugId) loadedDrugDetails.delete(variantDrugId); // invalidate level-2 cache
         await loadDrugs();
         renderDrugs();
         const message = newPackPayloads.length > 0
@@ -2574,6 +2626,7 @@ async function handleEditDrug(e) {
         if (!response.ok) throw new Error('Failed to update drug');
 
         closeEditModal();
+        loadedDrugDetails.delete(drugId); // invalidate level-2 cache
         await loadDrugs();
         showToast('Drug updated successfully!', 'success');
     } catch (error) {
@@ -2602,6 +2655,8 @@ async function deleteDrug(drugId) {
             throw new Error(error.detail || 'Failed to delete drug');
         }
 
+        loadedDrugDetails.delete(drugId); // invalidate level-2 cache
+        loadedVariantBatches.clear(); // variants of this drug are gone
         await loadDrugs();
         showToast('Drug deleted successfully!', 'success');
     } catch (error) {
@@ -3039,6 +3094,7 @@ async function handleBatchReceive(e) {
         
         document.getElementById('batchReceiveForm').reset();
         closeModal(document.getElementById('batchReceiveModal'));
+        loadedVariantBatches.delete(variantId); // invalidate level-3 cache
         await loadDrugs();
         showToast('Batch received successfully!', 'success');
     } catch (error) {
@@ -3052,6 +3108,12 @@ function getActiveDeliveryDrug() {
 }
 
 function getVariantById(variantId) {
+    // Prefer loaded drug details (have packs)
+    for (const detail of loadedDrugDetails.values()) {
+        const found = (detail.variants || []).find(v => v.id === variantId);
+        if (found) return found;
+    }
+    // Fall back to summary variant (no packs)
     for (const drug of allDrugs) {
         const found = (drug.variants || []).find(v => v.id === variantId);
         if (found) return found;
@@ -3059,6 +3121,18 @@ function getVariantById(variantId) {
     return null;
 }
 
+async function ensureDrugDetailLoaded(drugId) {
+    if (!drugId || loadedDrugDetails.has(drugId)) return;
+    try {
+        const response = await apiCall(`/drugs/${drugId}`);
+        if (response.ok) {
+            loadedDrugDetails.set(drugId, await response.json());
+        }
+    } catch (error) {
+        console.error(`Failed to load drug detail for drug ${drugId}:`, error);
+    }
+}
+
 function buildDeliveryVariantOptions(drug, selectedVariantId = '') {
     if (!drug || !drug.variants || drug.variants.length === 0) {
         return '<option value="">-- No variants available --</option>';
@@ -3116,8 +3190,9 @@ function wireDeliveryLineEvents(line) {
     const packCountInput = line.querySelector('.delivery-pack-count');
 
     if (drugSelect && variantSelect) {
-        drugSelect.addEventListener('change', () => {
+        drugSelect.addEventListener('change', async () => {
             const drugId = parseInt(drugSelect.value || '', 10);
+            await ensureDrugDetailLoaded(drugId);
             const drug = allDrugs.find(d => d.id === drugId) || null;
             variantSelect.innerHTML = buildDeliveryVariantOptions(drug, '');
             if (packSelect) packSelect.innerHTML = buildDeliveryPackOptions(null, '');
@@ -3466,7 +3541,7 @@ function _refreshGtinMappingSelects() {
 
 // Reinitialise the GTIN mapping modal dropdowns from fresh allDrugs data,
 // optionally pre-selecting specific drug/variant/pack IDs.
-function _reinitGtinMappingModal(restore) {
+async function _reinitGtinMappingModal(restore) {
     const drugSelect = document.getElementById('gtinMappingDrugSelect');
     const variantSelect = document.getElementById('gtinMappingVariantSelect');
     const packSelect = document.getElementById('gtinMappingPackSelect');
@@ -3488,6 +3563,7 @@ function _reinitGtinMappingModal(restore) {
     }
 
     drugSelect.value = String(drugId);
+    await ensureDrugDetailLoaded(drugId);
     const drug = allDrugs.find(d => d.id === drugId);
 
     // Rebuild variant list
@@ -3504,7 +3580,7 @@ function _reinitGtinMappingModal(restore) {
     }
 
     variantSelect.value = String(variantId);
-    const variant = drug?.variants?.find(v => v.id === variantId);
+    const variant = getVariantById(variantId); // checks loadedDrugDetails first (has packs)
 
     // Rebuild pack list
     packSelect.innerHTML = '<option value="">-- Select pack --</option>';
@@ -3540,9 +3616,9 @@ function gtinMappingAddPack() {
     const variantId = parseInt(document.getElementById('gtinMappingVariantSelect').value || '', 10);
     if (!variantId) { showToast('Select a variant first', 'warning'); return; }
     const drugId = parseInt(document.getElementById('gtinMappingDrugSelect').value || '', 10);
-    const drug = allDrugs.find(d => d.id === drugId);
-    if (!drug) return;
-    const variant = drug.variants?.find(v => v.id === variantId);
+    if (!drugId) return;
+    // Use getVariantById which returns the detail variant (with packs) if loaded
+    const variant = getVariantById(variantId);
     const existingPackIds = new Set((getActivePacksForVariant(variant) || []).map(p => p.id));
     _gtinMappingPendingRestore = { drugId, variantId, packId: null, _existingPackIds: existingPackIds };
     _gtinMappingPendingRefresh = true;
@@ -3571,15 +3647,17 @@ function openGtinMappingModal(gtin, expiryStr, lot) {
     openModal(document.getElementById('gtinMappingModal'));
 }
 
-function onGtinMappingDrugChange() {
+async function onGtinMappingDrugChange() {
     const drugId = parseInt(document.getElementById('gtinMappingDrugSelect').value || '', 10);
-    const drug = allDrugs.find(d => d.id === drugId);
     const variantSelect = document.getElementById('gtinMappingVariantSelect');
     const packSelect = document.getElementById('gtinMappingPackSelect');
 
     variantSelect.innerHTML = '<option value="">-- Select variant --</option>';
     packSelect.innerHTML = '<option value="">-- Select pack --</option>';
 
+    if (!drugId) return;
+    await ensureDrugDetailLoaded(drugId);
+    const drug = allDrugs.find(d => d.id === drugId);
     if (!drug) return;
     variantSelect.innerHTML += drug.variants.map(v =>
         `<option value="${v.id}">${escapeHtml(v.strength)} (${escapeHtml(v.unit)})</option>`
@@ -3587,10 +3665,8 @@ function onGtinMappingDrugChange() {
 }
 
 function onGtinMappingVariantChange() {
-    const drugId = parseInt(document.getElementById('gtinMappingDrugSelect').value || '', 10);
     const variantId = parseInt(document.getElementById('gtinMappingVariantSelect').value || '', 10);
-    const drug = allDrugs.find(d => d.id === drugId);
-    const variant = drug?.variants?.find(v => v.id === variantId);
+    const variant = getVariantById(variantId); // checks loadedDrugDetails first (has packs)
     const packSelect = document.getElementById('gtinMappingPackSelect');
 
     packSelect.innerHTML = '<option value="">-- Select pack --</option>';
@@ -3901,6 +3977,9 @@ async function handleAddPackSize(e) {
         }
 
         closeModal(document.getElementById('addPackSizeModal'));
+        // Invalidate drug detail cache so the new pack will be re-fetched on next expand
+        const packDrugId = allDrugs.find(d => (d.variants || []).some(v => v.id === variantId))?.id;
+        if (packDrugId) loadedDrugDetails.delete(packDrugId);
         await loadDrugs();
         // Refresh delivery line pack selects so the new pack is immediately available
         refreshDeliveryVariantSelects();
@@ -3986,6 +4065,8 @@ async function handleReceiveDelivery(e) {
 
         closeModal(document.getElementById('receiveDeliveryModal'));
         _detachDeliveryBarcodeListener();
+        // Invalidate batch cache for all delivered variants
+        payloads.forEach(entry => loadedVariantBatches.delete(entry.variantId));
         await loadDrugs();
         showToast(`Delivery received successfully (${payloads.length} line${payloads.length === 1 ? '' : 's'})`, 'success');
     } catch (error) {