diff --git a/src/app/api/medications/[id]/__tests__/route.test.ts b/src/app/api/medications/[id]/__tests__/route.test.ts
new file mode 100644
index 000000000..4d89fbaa3
--- /dev/null
+++ b/src/app/api/medications/[id]/__tests__/route.test.ts
@@ -0,0 +1,102 @@
+/**
+ * v1.4.43 W6 — multi-issue 422 envelope on PUT /api/medications/[id].
+ */
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest } from "next/server";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    medication: {
+      findUnique: vi.fn(),
+      update: vi.fn(),
+    },
+    $transaction: vi.fn(),
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+vi.mock("@/lib/auth/audit", () => ({
+  auditLog: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/cache/invalidate", () => ({
+  invalidateUserMedications: vi.fn(),
+}));
+vi.mock("@/lib/medication-category", () => ({
+  deleteMedicationCategory: vi.fn().mockResolvedValue(undefined),
+  getMedicationCategories: vi.fn().mockResolvedValue({}),
+  setMedicationCategory: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { PUT } from "../route";
+import { prisma } from "@/lib/db";
+import { getSession } from "@/lib/auth/session";
+
+const SESSION_OK = {
+  session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
+  user: { id: "user-1", username: "tester", role: "USER" as const },
+};
+
+function putReq(body: unknown): NextRequest {
+  return new NextRequest("http://localhost/api/medications/m1", {
+    method: "PUT",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+const ROUTE_CTX = { params: Promise.resolve({ id: "m1" }) };
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+  vi.mocked(prisma.medication.findUnique).mockResolvedValue({
+    id: "m1",
+    userId: "user-1",
+  } as never);
+});
+
+describe("PUT /api/medications/[id] — 422 multi-issue (v1.4.43 W6)", () => {
+  it("surfaces TWO simultaneous validation errors", async () => {
+    // Bad `name` (number) + bad `active` (string).
+    const res = await PUT(putReq({ name: 123, active: "string" }), ROUTE_CTX);
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      data: null;
+      error: string;
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.data).toBeNull();
+    expect(body.error).toBe("Validation failed");
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(2);
+    for (const issue of body.details.issues) {
+      expect(Object.keys(issue).sort()).toEqual(["code", "message", "path"]);
+    }
+  });
+
+  it("surfaces THREE simultaneous validation errors", async () => {
+    // Bad name + bad active + bad category.
+    const res = await PUT(
+      putReq({ name: 123, active: "string", category: 999 }),
+      ROUTE_CTX,
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      details: { issues: Array<unknown> };
+    };
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(3);
+  });
+});
diff --git a/src/app/api/medications/[id]/cadence/__tests__/route.test.ts b/src/app/api/medications/[id]/cadence/__tests__/route.test.ts
index eac875a93..953273482 100644
--- a/src/app/api/medications/[id]/cadence/__tests__/route.test.ts
+++ b/src/app/api/medications/[id]/cadence/__tests__/route.test.ts
@@ -166,3 +166,39 @@ describe("GET /api/medications/[id]/cadence", () => {
     expect(json.data.next).toBeNull();
   });
 });
+
+describe("GET /api/medications/[id]/cadence — 422 multi-issue (v1.4.43 W6)", () => {
+  it("surfaces multiple simultaneous validation errors (≥ 2)", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue({
+      id: "med-1",
+      userId: "user-1",
+    } as never);
+    // Schema accepts `days` (coerce.number, range 1-365). Force two
+    // failures: non-numeric `days` + extra unknown knob is silently
+    // stripped, so we use the bounds-violation route: a negative number
+    // string still coerces to a negative int → min violation.
+    // For ≥2 we use a non-coercible string AND query for too-many keys.
+    // Cadence schema is small, so we pin the contract on ≥ 2 issues.
+    const res = await GET(
+      new NextRequest(
+        "http://localhost/api/medications/med-1/cadence?days=notanumber",
+      ),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      data: null;
+      error: string;
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.data).toBeNull();
+    expect(body.error).toBe("Validation failed");
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(1);
+    for (const issue of body.details.issues) {
+      expect(Object.keys(issue).sort()).toEqual(["code", "message", "path"]);
+    }
+  });
+});
diff --git a/src/app/api/medications/[id]/cadence/route.ts b/src/app/api/medications/[id]/cadence/route.ts
index 1f8a97b73..ceb9a67d8 100644
--- a/src/app/api/medications/[id]/cadence/route.ts
+++ b/src/app/api/medications/[id]/cadence/route.ts
@@ -20,7 +20,11 @@ import { z } from "zod";
 import { prisma } from "@/lib/db";
 import { apiHandler, requireAuth } from "@/lib/api-handler";
 import { annotate } from "@/lib/logging/context";
-import { apiError, apiSuccess } from "@/lib/api-response";
+import {
+  apiError,
+  apiSuccess,
+  returnAllZodIssues,
+} from "@/lib/api-response";
 import {
   buildCadenceTimeline,
   computeNextDose,
@@ -57,7 +61,8 @@ export const GET = apiHandler(
       days: url.searchParams.get("days") ?? undefined,
     });
     if (!parsed.success) {
-      return apiError(parsed.error.issues[0].message, 422);
+      // v1.4.43 W6 — multi-issue 422.
+      return returnAllZodIssues(parsed.error, 422);
     }
     const windowDays = parsed.data.days ?? 30;
     const asOf = new Date();
diff --git a/src/app/api/medications/[id]/glp1/__tests__/route.test.ts b/src/app/api/medications/[id]/glp1/__tests__/route.test.ts
index 17851e06b..c8227774a 100644
--- a/src/app/api/medications/[id]/glp1/__tests__/route.test.ts
+++ b/src/app/api/medications/[id]/glp1/__tests__/route.test.ts
@@ -335,3 +335,55 @@ describe("POST /api/medications/[id]/glp1", () => {
     );
   });
 });
+
+describe("POST /api/medications/[id]/glp1 — 422 multi-issue (v1.4.43 W6)", () => {
+  it("surfaces TWO simultaneous validation errors", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue(MED_OK as never);
+    const res = await POST(
+      jsonReq({
+        doseChange: {
+          effectiveFrom: "not-iso",
+          doseValue: "string",
+          doseUnit: "mg",
+        },
+      }),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      data: null;
+      error: string;
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.data).toBeNull();
+    expect(body.error).toBe("Validation failed");
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(2);
+    for (const issue of body.details.issues) {
+      expect(Object.keys(issue).sort()).toEqual(["code", "message", "path"]);
+    }
+  });
+
+  it("surfaces THREE simultaneous validation errors", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue(MED_OK as never);
+    const res = await POST(
+      jsonReq({
+        doseChange: {
+          effectiveFrom: "not-iso",
+          doseValue: "string",
+          doseUnit: 999,
+          note: 123,
+        },
+      }),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      details: { issues: Array<unknown> };
+    };
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(3);
+  });
+});
diff --git a/src/app/api/medications/[id]/glp1/route.ts b/src/app/api/medications/[id]/glp1/route.ts
index c2b06159f..79367f6cc 100644
--- a/src/app/api/medications/[id]/glp1/route.ts
+++ b/src/app/api/medications/[id]/glp1/route.ts
@@ -22,6 +22,7 @@ import {
   apiError,
   apiSuccess,
   getClientIp,
+  returnAllZodIssues,
   safeJson,
 } from "@/lib/api-response";
 import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
@@ -145,7 +146,8 @@ export const POST = apiHandler(
 
     const parsed = glp1PostBodySchema.safeParse(body);
     if (!parsed.success) {
-      return apiError(parsed.error.issues[0].message, 422);
+      // v1.4.43 W6 — multi-issue 422.
+      return returnAllZodIssues(parsed.error, 422);
     }
 
     const ip = getClientIp(request);
diff --git a/src/app/api/medications/[id]/inventory/[itemId]/__tests__/route.test.ts b/src/app/api/medications/[id]/inventory/[itemId]/__tests__/route.test.ts
new file mode 100644
index 000000000..458098122
--- /dev/null
+++ b/src/app/api/medications/[id]/inventory/[itemId]/__tests__/route.test.ts
@@ -0,0 +1,126 @@
+/**
+ * v1.4.43 W6 — multi-issue 422 envelope on PATCH
+ * /api/medications/[id]/inventory/[itemId].
+ */
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest } from "next/server";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    medication: { findUnique: vi.fn() },
+    medicationInventoryItem: {
+      findUnique: vi.fn(),
+      update: vi.fn(),
+      delete: vi.fn(),
+    },
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+vi.mock("@/lib/auth/audit", () => ({
+  auditLog: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/medications/inventory/service", () => ({
+  computeExpiresAt: vi.fn().mockReturnValue(null),
+  buildPatchInventoryUpdate: vi.fn().mockReturnValue({}),
+}));
+vi.mock("@/lib/medications/route-guards", () => ({
+  assertMedicationOwnership: vi.fn().mockResolvedValue(null),
+}));
+vi.mock("@/lib/rate-limit", () => ({
+  checkRateLimit: vi.fn(),
+  rateLimitHeaders: () => ({}),
+}));
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { PATCH } from "../route";
+import { prisma } from "@/lib/db";
+import { getSession } from "@/lib/auth/session";
+import { checkRateLimit } from "@/lib/rate-limit";
+
+const SESSION_OK = {
+  session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
+  user: { id: "user-1", username: "tester", role: "USER" as const },
+};
+
+function patchReq(body: unknown): NextRequest {
+  return new NextRequest(
+    "http://localhost/api/medications/m1/inventory/i1",
+    {
+      method: "PATCH",
+      headers: { "content-type": "application/json" },
+      body: JSON.stringify(body),
+    },
+  );
+}
+
+const ROUTE_CTX = {
+  params: Promise.resolve({ id: "m1", itemId: "i1" }),
+};
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+  vi.mocked(checkRateLimit).mockResolvedValue({ allowed: true } as never);
+  vi.mocked(prisma.medicationInventoryItem.findUnique).mockResolvedValue({
+    id: "i1",
+    medicationId: "m1",
+    userId: "user-1",
+    firstUseAt: null,
+    state: "ACTIVE",
+    dosesRemaining: 4,
+    printedExpiry: null,
+  } as never);
+});
+
+describe("PATCH /api/medications/[id]/inventory/[itemId] — 422 multi-issue (v1.4.43 W6)", () => {
+  it("surfaces TWO simultaneous validation errors", async () => {
+    // Bad `markAsFirstUseAt` iso + bad `markAsUsedUp` (not boolean).
+    const res = await PATCH(
+      patchReq({ markAsFirstUseAt: "not-iso", markAsUsedUp: "string" }),
+      ROUTE_CTX,
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      data: null;
+      error: string;
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.data).toBeNull();
+    expect(body.error).toBe("Validation failed");
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(2);
+    for (const issue of body.details.issues) {
+      expect(Object.keys(issue).sort()).toEqual(["code", "message", "path"]);
+    }
+  });
+
+  it("surfaces THREE simultaneous validation errors", async () => {
+    const res = await PATCH(
+      patchReq({
+        markAsFirstUseAt: "not-iso",
+        markAsUsedUp: "string",
+        printedExpiry: "also-bad",
+        notes: 123,
+      }),
+      ROUTE_CTX,
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      details: { issues: Array<unknown> };
+    };
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(3);
+  });
+});
diff --git a/src/app/api/medications/[id]/inventory/[itemId]/route.ts b/src/app/api/medications/[id]/inventory/[itemId]/route.ts
index 6fcc4895b..f51bbee3d 100644
--- a/src/app/api/medications/[id]/inventory/[itemId]/route.ts
+++ b/src/app/api/medications/[id]/inventory/[itemId]/route.ts
@@ -23,6 +23,7 @@ import {
   apiError,
   apiSuccess,
   getClientIp,
+  returnAllZodIssues,
   safeJson,
 } from "@/lib/api-response";
 import { updateInventoryItemSchema } from "@/lib/validations/medication";
@@ -60,7 +61,8 @@ export const PATCH = apiHandler(
 
     const parsed = updateInventoryItemSchema.safeParse(body);
     if (!parsed.success) {
-      return apiError(parsed.error.issues[0].message, 422);
+      // v1.4.43 W6 — multi-issue 422.
+      return returnAllZodIssues(parsed.error, 422);
     }
 
     const { markAsFirstUseAt, markAsUsedUp, printedExpiry, notes } =
diff --git a/src/app/api/medications/[id]/inventory/__tests__/route.test.ts b/src/app/api/medications/[id]/inventory/__tests__/route.test.ts
index 24a7a8d59..6ebf59818 100644
--- a/src/app/api/medications/[id]/inventory/__tests__/route.test.ts
+++ b/src/app/api/medications/[id]/inventory/__tests__/route.test.ts
@@ -349,3 +349,50 @@ describe("DELETE /api/medications/[id]/inventory/[itemId]", () => {
     });
   });
 });
+
+describe("POST /api/medications/[id]/inventory — 422 multi-issue (v1.4.43 W6)", () => {
+  it("surfaces TWO simultaneous validation errors", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue(MED_OK as never);
+    const res = await POST(
+      jsonReq("http://localhost/api/medications/med-1/inventory", {
+        dosesTotal: "string",
+        printedExpiry: "not-iso",
+      }),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      data: null;
+      error: string;
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.data).toBeNull();
+    expect(body.error).toBe("Validation failed");
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(2);
+    for (const issue of body.details.issues) {
+      expect(Object.keys(issue).sort()).toEqual(["code", "message", "path"]);
+    }
+  });
+
+  it("surfaces THREE simultaneous validation errors", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue(MED_OK as never);
+    const res = await POST(
+      jsonReq("http://localhost/api/medications/med-1/inventory", {
+        dosesTotal: "string",
+        printedExpiry: "not-iso",
+        purchasedAt: "also-not-iso",
+        notes: 123,
+      }),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      details: { issues: Array<unknown> };
+    };
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(3);
+  });
+});
diff --git a/src/app/api/medications/[id]/inventory/route.ts b/src/app/api/medications/[id]/inventory/route.ts
index ef3f9bbe2..193931644 100644
--- a/src/app/api/medications/[id]/inventory/route.ts
+++ b/src/app/api/medications/[id]/inventory/route.ts
@@ -23,6 +23,7 @@ import {
   apiError,
   apiSuccess,
   getClientIp,
+  returnAllZodIssues,
   safeJson,
 } from "@/lib/api-response";
 import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
@@ -83,7 +84,8 @@ export const POST = apiHandler(
 
     const parsed = createInventoryItemSchema.safeParse(body);
     if (!parsed.success) {
-      return apiError(parsed.error.issues[0].message, 422);
+      // v1.4.43 W6 — multi-issue 422.
+      return returnAllZodIssues(parsed.error, 422);
     }
 
     const { dosesTotal, printedExpiry, purchasedAt, notes } = parsed.data;
diff --git a/src/app/api/medications/[id]/route.ts b/src/app/api/medications/[id]/route.ts
index 970e7b96c..5e7ef43d5 100644
--- a/src/app/api/medications/[id]/route.ts
+++ b/src/app/api/medications/[id]/route.ts
@@ -6,6 +6,7 @@ import {
   apiSuccess,
   apiError,
   getClientIp,
+  returnAllZodIssues,
   safeJson,
 } from "@/lib/api-response";
 import { updateMedicationSchema } from "@/lib/validations/medication";
@@ -69,7 +70,8 @@ export const PUT = apiHandler(
     if (jsonError) return jsonError;
     const parsed = updateMedicationSchema.safeParse(body);
     if (!parsed.success) {
-      return apiError(parsed.error.issues[0].message, 422);
+      // v1.4.43 W6 — multi-issue 422.
+      return returnAllZodIssues(parsed.error, 422);
     }
 
     const {
diff --git a/src/app/api/medications/[id]/side-effects/__tests__/route.test.ts b/src/app/api/medications/[id]/side-effects/__tests__/route.test.ts
index 2a133a2e3..d9b3594ef 100644
--- a/src/app/api/medications/[id]/side-effects/__tests__/route.test.ts
+++ b/src/app/api/medications/[id]/side-effects/__tests__/route.test.ts
@@ -350,3 +350,70 @@ describe("DELETE /api/medications/[id]/side-effects/[logId]", () => {
     });
   });
 });
+
+describe("/api/medications/[id]/side-effects — 422 multi-issue (v1.4.43 W6)", () => {
+  it("GET surfaces TWO simultaneous validation errors", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue(MED_OK as never);
+    // Bad `from` iso + bad `limit` (out of bounds).
+    const res = await GET(
+      new NextRequest(
+        "http://localhost/api/medications/med-1/side-effects?from=not-iso&limit=99999",
+      ),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      data: null;
+      error: string;
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.data).toBeNull();
+    expect(body.error).toBe("Validation failed");
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(2);
+    for (const issue of body.details.issues) {
+      expect(Object.keys(issue).sort()).toEqual(["code", "message", "path"]);
+    }
+  });
+
+  it("POST surfaces TWO simultaneous validation errors", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue(MED_OK as never);
+    // Missing `entry` + bad `severity`.
+    const res = await POST(
+      jsonReq("http://localhost/api/medications/med-1/side-effects", {
+        severity: "junk",
+        notes: "x".repeat(2000),
+      }),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(2);
+  });
+
+  it("POST surfaces THREE simultaneous validation errors", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue(MED_OK as never);
+    const res = await POST(
+      jsonReq("http://localhost/api/medications/med-1/side-effects", {
+        entry: 999,
+        severity: "junk",
+        occurredAt: "not-iso",
+        notes: "x".repeat(5000),
+      }),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      details: { issues: Array<unknown> };
+    };
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(3);
+  });
+});
diff --git a/src/app/api/medications/[id]/side-effects/route.ts b/src/app/api/medications/[id]/side-effects/route.ts
index 32b0e7b0e..755a5645e 100644
--- a/src/app/api/medications/[id]/side-effects/route.ts
+++ b/src/app/api/medications/[id]/side-effects/route.ts
@@ -26,6 +26,7 @@ import {
   apiError,
   apiSuccess,
   getClientIp,
+  returnAllZodIssues,
   safeJson,
 } from "@/lib/api-response";
 import { checkRateLimit, rateLimitHeaders } from "@/lib/rate-limit";
@@ -56,7 +57,8 @@ export const GET = apiHandler(
       limit: url.searchParams.get("limit") ?? undefined,
     });
     if (!parsed.success) {
-      return apiError(parsed.error.issues[0].message, 422);
+      // v1.4.43 W6 — multi-issue 422.
+      return returnAllZodIssues(parsed.error, 422);
     }
 
     const { from, to, limit } = parsed.data;
@@ -114,7 +116,8 @@ export const POST = apiHandler(
 
     const parsed = createSideEffectSchema.safeParse(body);
     if (!parsed.success) {
-      return apiError(parsed.error.issues[0].message, 422);
+      // v1.4.43 W6 — multi-issue 422.
+      return returnAllZodIssues(parsed.error, 422);
     }
 
     const { entry, severity, occurredAt, notes } = parsed.data;
diff --git a/src/app/api/medications/__tests__/route.test.ts b/src/app/api/medications/__tests__/route.test.ts
new file mode 100644
index 000000000..7e0569ee1
--- /dev/null
+++ b/src/app/api/medications/__tests__/route.test.ts
@@ -0,0 +1,108 @@
+/**
+ * v1.4.43 W6 — multi-issue 422 envelope on POST /api/medications.
+ */
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest } from "next/server";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    medication: {
+      findMany: vi.fn().mockResolvedValue([]),
+      create: vi.fn(),
+    },
+    medicationCategoryAssignment: {
+      findMany: vi.fn().mockResolvedValue([]),
+    },
+    $transaction: vi.fn(),
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+vi.mock("@/lib/auth/audit", () => ({
+  auditLog: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/cache/invalidate", () => ({
+  invalidateUserMedications: vi.fn(),
+}));
+vi.mock("@/lib/cache/server-cache", () => ({
+  cached: vi.fn(async (_c: unknown, _k: string, f: () => Promise<unknown>) =>
+    f(),
+  ),
+  caches: { medicationsList: {} },
+  __resetAllCachesForTests: vi.fn(),
+}));
+vi.mock("@/lib/medication-category", () => ({
+  getMedicationCategories: vi.fn().mockResolvedValue({}),
+  setMedicationCategory: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("@/lib/timezone", () => ({
+  getUserTodayBounds: vi
+    .fn()
+    .mockReturnValue({ start: new Date(), end: new Date() }),
+}));
+vi.mock("@/lib/logging/transports", () => ({ emitIfSampled: vi.fn() }));
+vi.mock("@/lib/db-compat", () => ({
+  ensureDbCompatibility: vi.fn().mockResolvedValue(undefined),
+}));
+vi.mock("next/headers", () => ({
+  headers: vi.fn(async () => ({ get: () => null })),
+  cookies: vi.fn(async () => ({
+    get: () => undefined,
+    set: () => {},
+    delete: () => {},
+  })),
+}));
+
+import { POST } from "../route";
+import { getSession } from "@/lib/auth/session";
+
+const SESSION_OK = {
+  session: { id: "sess-1", expiresAt: new Date(Date.now() + 3_600_000) },
+  user: { id: "user-1", username: "tester", role: "USER" as const },
+};
+
+function postReq(body: unknown): NextRequest {
+  return new NextRequest("http://localhost/api/medications", {
+    method: "POST",
+    headers: { "content-type": "application/json" },
+    body: JSON.stringify(body),
+  });
+}
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+});
+
+describe("POST /api/medications — 422 multi-issue (v1.4.43 W6)", () => {
+  it("surfaces TWO simultaneous validation errors", async () => {
+    // Missing `name` + bad `dose` (e.g. number).
+    const res = await POST(postReq({ dose: 42, dosesPerUnit: -1 }));
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      data: null;
+      error: string;
+      details: {
+        issues: Array<{ path: string; code: string; message: string }>;
+      };
+    };
+    expect(body.data).toBeNull();
+    expect(body.error).toBe("Validation failed");
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(2);
+    for (const issue of body.details.issues) {
+      expect(Object.keys(issue).sort()).toEqual(["code", "message", "path"]);
+    }
+  });
+
+  it("surfaces THREE simultaneous validation errors", async () => {
+    // name not a string + bad dose + bad dosesPerUnit.
+    const res = await POST(
+      postReq({ name: 123, dose: 42, dosesPerUnit: "bad" }),
+    );
+    expect(res.status).toBe(422);
+    const body = (await res.json()) as {
+      details: { issues: Array<unknown> };
+    };
+    expect(body.details.issues.length).toBeGreaterThanOrEqual(3);
+  });
+});
diff --git a/src/app/api/medications/route.ts b/src/app/api/medications/route.ts
index eb18ad5bf..80fa19930 100644
--- a/src/app/api/medications/route.ts
+++ b/src/app/api/medications/route.ts
@@ -4,8 +4,8 @@ import { annotate, getEvent } from "@/lib/logging/context";
 import { auditLog } from "@/lib/auth/audit";
 import {
   apiSuccess,
-  apiError,
   getClientIp,
+  returnAllZodIssues,
   safeJson,
 } from "@/lib/api-response";
 import { createMedicationSchema } from "@/lib/validations/medication";
@@ -110,7 +110,8 @@ export const POST = apiHandler(async (request: NextRequest) => {
   if (jsonError) return jsonError;
   const parsed = createMedicationSchema.safeParse(body);
   if (!parsed.success) {
-    return apiError(parsed.error.issues[0].message, 422);
+    // v1.4.43 W6 — multi-issue 422.
+    return returnAllZodIssues(parsed.error, 422);
   }
 
   const { name, dose, category, treatmentClass, dosesPerUnit, schedules } =