diff --git a/src/lib/medications/inventory/__tests__/service.test.ts b/src/lib/medications/inventory/__tests__/service.test.ts
index 053a73e0e..1864a30c3 100644
--- a/src/lib/medications/inventory/__tests__/service.test.ts
+++ b/src/lib/medications/inventory/__tests__/service.test.ts
@@ -6,6 +6,7 @@ vi.mock("@/lib/db", () => ({
       findFirst: vi.fn(),
       findMany: vi.fn(),
       update: vi.fn(),
+      updateMany: vi.fn(),
     },
   },
 }));
@@ -122,36 +123,48 @@ describe("consumeOneDose", () => {
 });
 
 describe("expireStaleInUseItems", () => {
-  it("transitions IN_USE rows whose 30-day window has lapsed to EXPIRED", async () => {
-    const firstUseAgo = new Date(NOW.getTime() - 31 * MS_PER_DAY);
-    vi.mocked(prisma.medicationInventoryItem.findMany).mockResolvedValue([
-      {
-        id: "inv-stale",
-        state: "IN_USE",
-        dosesTotal: 4,
-        dosesRemaining: 2,
-        firstUseAt: firstUseAgo,
-        printedExpiry: null,
-      },
-    ] as never);
-    vi.mocked(prisma.medicationInventoryItem.update).mockResolvedValue({} as never);
+  it("transitions IN_USE rows whose deadline has lapsed via a single updateMany", async () => {
+    // The selector `state = IN_USE AND expiresAt < now` already proves
+    // the row must transition to EXPIRED (IN_USE implies dosesRemaining
+    // > 0, and the expiresAt filter proves the deadline lapsed). Using
+    // `updateMany` collapses N row round-trips into one.
+    vi.mocked(prisma.medicationInventoryItem.updateMany).mockResolvedValue({
+      count: 3,
+    } as never);
 
     const count = await expireStaleInUseItems({ nowMs: NOW.getTime() });
-    expect(count).toBe(1);
-    expect(prisma.medicationInventoryItem.update).toHaveBeenCalledWith({
-      where: { id: "inv-stale" },
+    expect(count).toBe(3);
+    expect(prisma.medicationInventoryItem.updateMany).toHaveBeenCalledTimes(1);
+    expect(prisma.medicationInventoryItem.updateMany).toHaveBeenCalledWith({
+      where: {
+        state: "IN_USE",
+        expiresAt: { lt: new Date(NOW.getTime()) },
+      },
+      data: { state: "EXPIRED" },
+    });
+    expect(prisma.medicationInventoryItem.update).not.toHaveBeenCalled();
+    expect(prisma.medicationInventoryItem.findMany).not.toHaveBeenCalled();
+  });
+
+  it("scopes to a single user when userId is given", async () => {
+    vi.mocked(prisma.medicationInventoryItem.updateMany).mockResolvedValue({
+      count: 0,
+    } as never);
+
+    await expireStaleInUseItems({ userId: "user-1", nowMs: NOW.getTime() });
+    expect(prisma.medicationInventoryItem.updateMany).toHaveBeenCalledWith({
+      where: expect.objectContaining({ userId: "user-1" }),
       data: { state: "EXPIRED" },
     });
   });
 
-  it("scopes to a single user when userId is given", async () => {
-    vi.mocked(prisma.medicationInventoryItem.findMany).mockResolvedValue([] as never);
+  it("returns 0 when no rows match", async () => {
+    vi.mocked(prisma.medicationInventoryItem.updateMany).mockResolvedValue({
+      count: 0,
+    } as never);
 
-    await expireStaleInUseItems({ userId: "user-1", nowMs: NOW.getTime() });
-    expect(prisma.medicationInventoryItem.findMany).toHaveBeenCalledWith({
-      where: expect.objectContaining({ userId: "user-1" }),
-      select: expect.anything(),
-    });
+    const count = await expireStaleInUseItems({ nowMs: NOW.getTime() });
+    expect(count).toBe(0);
   });
 });
 
diff --git a/src/lib/medications/inventory/service.ts b/src/lib/medications/inventory/service.ts
index 5ea29193e..58e9f8bc7 100644
--- a/src/lib/medications/inventory/service.ts
+++ b/src/lib/medications/inventory/service.ts
@@ -9,7 +9,6 @@
 import { prisma } from "@/lib/db";
 import {
   computeExpiresAt,
-  computeInventoryState,
   decrementDose,
   type DecrementOutcome,
 } from "./state-machine";
@@ -108,35 +107,25 @@ export async function expireStaleInUseItems(input: {
   const { userId, nowMs } = input;
   const now = new Date(nowMs);
 
-  // Candidates: IN_USE rows whose expiresAt has lapsed. EXPIRED rows
-  // are already terminal; USED_UP rows are off-window by definition.
-  const candidates = await prisma.medicationInventoryItem.findMany({
+  // Candidates: IN_USE rows whose `expiresAt` has lapsed. The
+  // selector + state-machine semantics line up here — every row that
+  // matches `state = IN_USE AND expiresAt < now` is also a row that
+  // `computeInventoryState` would classify EXPIRED (clause 2 or 3),
+  // because IN_USE implies `dosesRemaining > 0` (decrementDose flips
+  // an empty pen to USED_UP) and the `expiresAt` filter already
+  // proves the printed-expiry-or-window deadline has lapsed. EXPIRED
+  // rows are already terminal; USED_UP rows are off-window by
+  // definition. Use a single `updateMany` instead of one update per
+  // row — the daily cron sweep ran N round-trips for nothing.
+  const result = await prisma.medicationInventoryItem.updateMany({
     where: {
       state: "IN_USE",
       expiresAt: { lt: now },
       ...(userId ? { userId } : {}),
     },
-    select: {
-      id: true,
-      state: true,
-      dosesTotal: true,
-      dosesRemaining: true,
-      firstUseAt: true,
-      printedExpiry: true,
-    },
+    data: { state: "EXPIRED" },
   });
-
-  let transitions = 0;
-  for (const row of candidates) {
-    const nextState = computeInventoryState(row, nowMs);
-    if (nextState === row.state) continue;
-    await prisma.medicationInventoryItem.update({
-      where: { id: row.id },
-      data: { state: nextState },
-    });
-    transitions += 1;
-  }
-  return transitions;
+  return result.count;
 }
 
 /**