diff --git a/src/app/api/medications/[id]/cadence/__tests__/route.test.ts b/src/app/api/medications/[id]/cadence/__tests__/route.test.ts
new file mode 100644
index 000000000..eac875a93
--- /dev/null
+++ b/src/app/api/medications/[id]/cadence/__tests__/route.test.ts
@@ -0,0 +1,168 @@
+/**
+ * v1.4.25 W19e — cadence + compliance API route tests.
+ *
+ * Mirrors the W19d side-effect test fixture pattern: external
+ * dependencies are mocked at module boundaries (Prisma, session,
+ * logging transport), and each test pins one contract case.
+ */
+
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { NextRequest } from "next/server";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    medication: { findUnique: vi.fn() },
+    medicationIntakeEvent: { findMany: vi.fn() },
+  },
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: vi.fn() }));
+
+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 { GET } 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: "marc", role: "USER" as const },
+};
+
+beforeEach(() => {
+  vi.resetAllMocks();
+});
+
+describe("GET /api/medications/[id]/cadence", () => {
+  it("returns 401 when unauthenticated", async () => {
+    vi.mocked(getSession).mockResolvedValue(null);
+    const res = await GET(
+      new NextRequest("http://localhost/api/medications/med-1/cadence"),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(401);
+  });
+
+  it("returns 404 when the medication is not owned by the caller", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue({
+      id: "med-1",
+      userId: "OTHER",
+      createdAt: new Date(),
+      schedules: [],
+    } as never);
+
+    const res = await GET(
+      new NextRequest("http://localhost/api/medications/med-1/cadence"),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(404);
+  });
+
+  it("returns 422 for an out-of-range days parameter", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue({
+      id: "med-1",
+      userId: "user-1",
+      createdAt: new Date(),
+      schedules: [],
+    } as never);
+
+    const res = await GET(
+      new NextRequest(
+        "http://localhost/api/medications/med-1/cadence?days=9999",
+      ),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(422);
+  });
+
+  it("returns the timeline + chips for an owned medication", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue({
+      id: "med-1",
+      userId: "user-1",
+      createdAt: new Date(Date.now() - 60 * 24 * 60 * 60 * 1000),
+      schedules: [
+        {
+          id: "sch-1",
+          medicationId: "med-1",
+          windowStart: "08:00",
+          windowEnd: "09:00",
+          label: null,
+          dose: null,
+          daysOfWeek: null,
+        },
+      ],
+    } as never);
+    vi.mocked(prisma.medicationIntakeEvent.findMany).mockResolvedValue([]);
+
+    const res = await GET(
+      new NextRequest(
+        "http://localhost/api/medications/med-1/cadence?days=14",
+      ),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(200);
+    const json = await res.json();
+    expect(json.data.windowDays).toBe(14);
+    expect(Array.isArray(json.data.timeline)).toBe(true);
+    expect(json.data.chips).toMatchObject({
+      adherenceRate: expect.anything(),
+      currentStreak: expect.any(Number),
+      longestStreak: expect.any(Number),
+      missedLast30: expect.any(Number),
+    });
+  });
+
+  it("defaults to a 30-day window when no `days` query param is supplied", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue({
+      id: "med-1",
+      userId: "user-1",
+      createdAt: new Date(Date.now() - 60 * 24 * 60 * 60 * 1000),
+      schedules: [],
+    } as never);
+    vi.mocked(prisma.medicationIntakeEvent.findMany).mockResolvedValue([]);
+
+    const res = await GET(
+      new NextRequest("http://localhost/api/medications/med-1/cadence"),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(200);
+    const json = await res.json();
+    expect(json.data.windowDays).toBe(30);
+  });
+
+  it("returns a `null` next-dose when no schedule expands in the lookahead", async () => {
+    vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
+    vi.mocked(prisma.medication.findUnique).mockResolvedValue({
+      id: "med-1",
+      userId: "user-1",
+      createdAt: new Date(Date.now() - 60 * 24 * 60 * 60 * 1000),
+      schedules: [],
+    } as never);
+    vi.mocked(prisma.medicationIntakeEvent.findMany).mockResolvedValue([]);
+
+    const res = await GET(
+      new NextRequest("http://localhost/api/medications/med-1/cadence"),
+      { params: Promise.resolve({ id: "med-1" }) },
+    );
+    expect(res.status).toBe(200);
+    const json = await res.json();
+    expect(json.data.next).toBeNull();
+  });
+});
diff --git a/src/app/api/medications/[id]/cadence/route.ts b/src/app/api/medications/[id]/cadence/route.ts
new file mode 100644
index 000000000..51e830c5b
--- /dev/null
+++ b/src/app/api/medications/[id]/cadence/route.ts
@@ -0,0 +1,128 @@
+/**
+ * v1.4.25 W19e — GLP-1 cadence + compliance read endpoint.
+ *
+ *   GET /api/medications/[id]/cadence?days=30
+ *     - returns the schedule's 30-day (configurable) expected-vs-actual
+ *       dose timeline plus the four compliance chip values that drive
+ *       the detail-page section.
+ *
+ * Pure computation — no writes. The route delegates math to the
+ * `src/lib/medications/scheduling/{cadence,compliance}` pure modules
+ * so the chart, the chips, and the server agree dose-for-dose.
+ *
+ * Auth: cookie-session via requireAuth(); the medication is verified
+ * to belong to the caller before any read.
+ */
+
+import { NextRequest } from "next/server";
+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 {
+  buildCadenceTimeline,
+  computeNextDose,
+} from "@/lib/medications/scheduling/cadence";
+import { complianceChips } from "@/lib/medications/scheduling/compliance";
+
+type RouteParams = { params: Promise<{ id: string }> };
+
+const querySchema = z.object({
+  days: z.coerce.number().int().min(1).max(180).optional(),
+});
+
+export const GET = apiHandler(
+  async (request: NextRequest, { params }: RouteParams) => {
+    const { user } = await requireAuth();
+    const { id } = await params;
+
+    const med = await prisma.medication.findUnique({
+      where: { id },
+      include: { schedules: true },
+    });
+    if (!med || med.userId !== user.id) {
+      return apiError("Medication not found", 404);
+    }
+
+    const url = new URL(request.url);
+    const parsed = querySchema.safeParse({
+      days: url.searchParams.get("days") ?? undefined,
+    });
+    if (!parsed.success) {
+      return apiError(parsed.error.issues[0].message, 422);
+    }
+    const windowDays = parsed.data.days ?? 30;
+    const asOf = new Date();
+
+    // Pull intake events covering the window + a small buffer so a dose
+    // logged at the edge can still pair with its slot.
+    const bufferMs = 24 * 60 * 60 * 1000;
+    const from = new Date(asOf.getTime() - windowDays * 24 * 60 * 60 * 1000 - bufferMs);
+    const events = await prisma.medicationIntakeEvent.findMany({
+      where: {
+        medicationId: id,
+        userId: user.id,
+        scheduledFor: { gte: from },
+      },
+      select: { scheduledFor: true, takenAt: true, skipped: true },
+      orderBy: { scheduledFor: "asc" },
+    });
+
+    // The cadence-anchor is the medication's createdAt for stable
+    // intervalWeeks=N phasing. Falling back to `from` would re-anchor
+    // every window-size change, which would make a 30-day vs 90-day
+    // chart disagree on the bi-weekly grid.
+    const anchor = med.createdAt;
+
+    const timeline = buildCadenceTimeline(
+      med.schedules,
+      events,
+      asOf,
+      windowDays,
+      anchor,
+    );
+    const chips = complianceChips(
+      med.schedules,
+      events,
+      asOf,
+      windowDays,
+      anchor,
+    );
+    const next = computeNextDose(med.schedules, asOf, 14, anchor);
+
+    annotate({
+      action: {
+        name: "medication.cadence",
+        entity_type: "medication",
+        entity_id: id,
+      },
+      meta: {
+        window_days: windowDays,
+        slots: timeline.length,
+        adherence: chips.adherenceRate,
+      },
+    });
+
+    return apiSuccess({
+      windowDays,
+      anchorIso: anchor.toISOString(),
+      next: next
+        ? {
+            windowStart: next.windowStart.toISOString(),
+            windowEnd: next.windowEnd.toISOString(),
+            scheduleIndex: next.scheduleIndex,
+          }
+        : null,
+      chips,
+      timeline: timeline.map((p) => ({
+        day: p.day.toISOString(),
+        windowStart: p.windowStart.toISOString(),
+        windowEnd: p.windowEnd.toISOString(),
+        scheduleIndex: p.scheduleIndex,
+        status: p.status,
+      })),
+    });
+  },
+);