diff --git a/src/lib/medications/__tests__/glp1-knowledge-drift.test.ts b/src/lib/medications/__tests__/glp1-knowledge-drift.test.ts
new file mode 100644
index 000000000..c0eced312
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+++ b/src/lib/medications/__tests__/glp1-knowledge-drift.test.ts
@@ -0,0 +1,225 @@
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+import { describe, expect, it } from "vitest";
+
+import { GLP1_DRUGS } from "@/lib/medications/glp1-knowledge";
+
+/**
+ * Drift guard for the GLP-1 knowledge layer.
+ *
+ * The research file `.planning/research/glp1-feature-inspiration.md`
+ * §1 + §2.6 is the single source of truth — every numeric parameter
+ * in `glp1-knowledge.ts` is cited there against an EMA EPAR PDF or
+ * the peer-reviewed pharmacometric paper (Schneck & Urva 2024,
+ * DOI 10.1002/psp4.13099).
+ *
+ * Two layers of guarantee:
+ *   1) Hard-coded expected values that match the cited primary
+ *      regulatory document — break if anyone edits the TS module
+ *      without a matching research-file update.
+ *   2) Soft pin against the research file itself — the test reads
+ *      the markdown and asserts the citation strings still appear,
+ *      so a research-file revision that *removes* a citation
+ *      surfaces immediately.
+ *
+ * Together: a refactor that mutates a half-life or shifts a Ka by
+ * a percent without a regulatory rationale fails the test before
+ * it reaches production. The clinical reading layer (Coach,
+ * inventory countdown, titration card) can trust the catalog.
+ */
+
+const RESEARCH_PATH = join(
+  __dirname,
+  "../../../../.planning/research/glp1-feature-inspiration.md",
+);
+
+const RESEARCH_TEXT = readFileSync(RESEARCH_PATH, "utf8");
+
+/** Hard pins — these are the exact values the research file cites
+ *  against EMA EPAR / psp4.13099. If you change the TS module, you
+ *  must update both halves: this test and the research file. */
+const HARD_PINS = [
+  {
+    id: "tirzepatide",
+    halfLifeDays: 5.0,
+    bioavailability: 0.8,
+    absorptionRateHourlyKa: 0.0373,
+    clearanceLPerHour70kg: 0.0329,
+    compartmentModel: "two-compartment",
+    citation: "Schneck",
+    citationDoi: "10.1002/psp4.13099",
+    titrationStepsMg: [2.5, 5, 7.5, 10, 12.5, 15],
+    inUseMaxDays: 30,
+  },
+  {
+    id: "semaglutide",
+    halfLifeDays: 7.0,
+    bioavailability: 0.89,
+    compartmentModel: "two-compartment",
+    inUseMaxDays: 56,
+  },
+  {
+    id: "liraglutide",
+    // 13 h per EMA EPAR §5.2 — stored as fractional days.
+    halfLifeHoursApprox: 13,
+    bioavailability: 0.55,
+  },
+  {
+    id: "dulaglutide",
+    halfLifeDays: 5.0,
+    // 47–65 % range; record carries the lower bound.
+    bioavailability: 0.47,
+  },
+  {
+    id: "exenatide",
+    // Byetta IR ~2.4 h per EMA EPAR §5.2.
+    halfLifeHoursApprox: 2.4,
+    bioavailability: 0.65,
+  },
+] as const;
+
+describe("glp1-knowledge drift guard", () => {
+  describe("TS module values vs cited primary sources", () => {
+    for (const pin of HARD_PINS) {
+      describe(pin.id, () => {
+        const record = GLP1_DRUGS[pin.id as keyof typeof GLP1_DRUGS];
+
+        if ("halfLifeDays" in pin && pin.halfLifeDays !== undefined) {
+          it(`pins half-life to ${pin.halfLifeDays} d`, () => {
+            expect(record.pharmacology.halfLifeDays).toBe(pin.halfLifeDays);
+          });
+        }
+
+        if ("halfLifeHoursApprox" in pin) {
+          it(`pins half-life within rounding of ${pin.halfLifeHoursApprox} h`, () => {
+            expect(record.pharmacology.halfLifeDays * 24).toBeCloseTo(
+              pin.halfLifeHoursApprox,
+              1,
+            );
+          });
+        }
+
+        if ("bioavailability" in pin) {
+          it(`pins bioavailability to ${pin.bioavailability}`, () => {
+            expect(record.pharmacology.bioavailability).toBe(pin.bioavailability);
+          });
+        }
+
+        if ("absorptionRateHourlyKa" in pin && pin.absorptionRateHourlyKa !== undefined) {
+          it(`pins Ka to ${pin.absorptionRateHourlyKa} h⁻¹ (psp4.13099 Table 3)`, () => {
+            expect(record.pharmacology.absorptionRateHourlyKa).toBe(
+              pin.absorptionRateHourlyKa,
+            );
+          });
+        }
+
+        if ("clearanceLPerHour70kg" in pin && pin.clearanceLPerHour70kg !== undefined) {
+          it(`pins CL to ${pin.clearanceLPerHour70kg} L/h per 70 kg`, () => {
+            expect(record.pharmacology.clearanceLPerHour70kg).toBe(
+              pin.clearanceLPerHour70kg,
+            );
+          });
+        }
+
+        if ("compartmentModel" in pin && pin.compartmentModel !== undefined) {
+          it(`pins compartment model to ${pin.compartmentModel}`, () => {
+            expect(record.pharmacology.compartmentModel).toBe(pin.compartmentModel);
+          });
+        }
+
+        if ("titrationStepsMg" in pin && pin.titrationStepsMg !== undefined) {
+          it("pins titration ladder to EMA EPAR §4.2 sequence", () => {
+            expect(record.titrationStepsMg).toEqual(pin.titrationStepsMg);
+          });
+        }
+
+        if ("inUseMaxDays" in pin && pin.inUseMaxDays !== undefined) {
+          it(`pins post-opening in-use window to ${pin.inUseMaxDays} d`, () => {
+            expect(record.storage.inUse.maxDays).toBe(pin.inUseMaxDays);
+          });
+        }
+
+        if ("citation" in pin && pin.citation !== undefined) {
+          it(`carries the ${pin.citation} citation`, () => {
+            expect(record.sourceJournal?.citation).toContain(pin.citation);
+          });
+        }
+
+        if ("citationDoi" in pin && pin.citationDoi !== undefined) {
+          it(`carries the DOI ${pin.citationDoi}`, () => {
+            expect(record.sourceJournal?.doi).toBe(pin.citationDoi);
+          });
+        }
+      });
+    }
+  });
+
+  describe("research-file citation presence", () => {
+    it("references the EMA Mounjaro EPAR for tirzepatide", () => {
+      expect(RESEARCH_TEXT).toMatch(/mounjaro-epar-product-information/);
+    });
+
+    it("references the Schneck/Urva 2024 paper for tirzepatide PK", () => {
+      expect(RESEARCH_TEXT).toMatch(/Schneck/);
+      expect(RESEARCH_TEXT).toMatch(/psp4\.13099/);
+    });
+
+    it("cites tirzepatide Ka 0.0373 h⁻¹ in §1.1 / §2.6", () => {
+      expect(RESEARCH_TEXT).toMatch(/0\.0373/);
+    });
+
+    it("cites tirzepatide CL 0.0329 L/h in §1.1 / §2.6", () => {
+      expect(RESEARCH_TEXT).toMatch(/0\.0329/);
+    });
+
+    it("cites the 30-day in-use KwikPen window in §1.1", () => {
+      expect(RESEARCH_TEXT).toMatch(/30 days/);
+    });
+
+    it("references the Ozempic EPAR for semaglutide", () => {
+      expect(RESEARCH_TEXT).toMatch(/ozempic-epar/);
+    });
+
+    it("references the Saxenda EPAR for liraglutide", () => {
+      expect(RESEARCH_TEXT).toMatch(/saxenda-epar/);
+    });
+
+    it("declares the N7 retatrutide exclusion explicitly", () => {
+      // Two phrasings appear in the research file; either is enough.
+      expect(
+        /retatrutide.*not approved|EMA approval|including it implies endorsement/i.test(
+          RESEARCH_TEXT,
+        ),
+      ).toBe(true);
+    });
+  });
+
+  describe("research-file presence checks for module values", () => {
+    it("agrees with the research file on tirzepatide half-life ≈ 5 days", () => {
+      // Research file's §1.1 + §2.6 both say "≈ 5 days" / "5.4 days"
+      // for tirzepatide. TS module pins 5.0. The numbers reconcile
+      // within psp4.13099's IIV (5.4 d journal vs ≈ 5 d EMA EPAR).
+      expect(GLP1_DRUGS.tirzepatide.pharmacology.halfLifeDays).toBeGreaterThanOrEqual(
+        5.0,
+      );
+      expect(GLP1_DRUGS.tirzepatide.pharmacology.halfLifeDays).toBeLessThanOrEqual(
+        5.5,
+      );
+      expect(RESEARCH_TEXT).toMatch(/(≈ 5 d|5 days|5\.4 d|5\.4 days)/);
+    });
+
+    it("agrees with the research file on semaglutide half-life ≈ 1 week", () => {
+      expect(GLP1_DRUGS.semaglutide.pharmacology.halfLifeDays).toBe(7);
+      expect(RESEARCH_TEXT).toMatch(/(≈ 1 week|half-life ≈ 1 week|7 days)/);
+    });
+
+    it("agrees with the research file on liraglutide half-life ≈ 13 h", () => {
+      expect(GLP1_DRUGS.liraglutide.pharmacology.halfLifeDays * 24).toBeCloseTo(
+        13,
+        1,
+      );
+      expect(RESEARCH_TEXT).toMatch(/(≈ 13 hours|13 h|half-life ≈ 13)/);
+    });
+  });
+});