diff --git a/src/lib/medications/side-effects/__tests__/drift-guard.test.ts b/src/lib/medications/side-effects/__tests__/drift-guard.test.ts
new file mode 100644
index 000000000..c404f67dd
--- /dev/null
+++ b/src/lib/medications/side-effects/__tests__/drift-guard.test.ts
@@ -0,0 +1,115 @@
+/**
+ * v1.4.25 W21 Fix-N (code-M1 + simp-M1) — drift guard.
+ *
+ * Three sources of truth historically described the side-effect enum:
+ *
+ *   1. The Prisma `MedicationSideEffectCategory` + `MedicationSideEffectEntry`
+ *      enums (DB-level CHECK constraints).
+ *   2. The taxonomy module (`SIDE_EFFECT_CATEGORIES` map + the
+ *      `SIDE_EFFECT_ENTRIES_BY_CATEGORY` grouping).
+ *   3. The Zod validators (`SIDE_EFFECT_CATEGORY_VALUES` /
+ *      `SIDE_EFFECT_ENTRY_VALUES`).
+ *
+ * Adding a new entry historically required touching all three; any
+ * single omission silently broke production (e.g. a Prisma migration
+ * adds a new value, but the Zod validator's tuple still rejects it on
+ * the wire → 422 surface that maps to a value the DB will gladly
+ * accept). Now the validators DERIVE from the Prisma enum, and this
+ * test asserts the three keysets stay in lockstep.
+ *
+ * If any of these assertions fail: a new entry was added in Prisma
+ * but the taxonomy map / category grouping wasn't updated — fix those
+ * before merging.
+ */
+
+import { describe, expect, it } from "vitest";
+
+import {
+  MedicationSideEffectCategory,
+  MedicationSideEffectEntry,
+} from "@/generated/prisma/client";
+import {
+  SIDE_EFFECT_CATEGORY_VALUES,
+  SIDE_EFFECT_ENTRY_VALUES,
+} from "../validators";
+import {
+  SIDE_EFFECT_CATEGORIES,
+  SIDE_EFFECT_CATEGORY_ORDER,
+  SIDE_EFFECT_ENTRIES_BY_CATEGORY,
+  SIDE_EFFECT_ENTRY_COUNT,
+} from "../taxonomy";
+
+function sortedKeys<T extends string>(keys: readonly T[]): T[] {
+  return [...keys].sort();
+}
+
+describe("side-effect taxonomy drift guard", () => {
+  describe("category keysets", () => {
+    it("validator categories equal Prisma enum categories", () => {
+      const prisma = Object.values(MedicationSideEffectCategory);
+      expect(sortedKeys(SIDE_EFFECT_CATEGORY_VALUES)).toEqual(
+        sortedKeys(prisma),
+      );
+    });
+
+    it("taxonomy category order equals Prisma enum categories", () => {
+      const prisma = Object.values(MedicationSideEffectCategory);
+      expect(sortedKeys(SIDE_EFFECT_CATEGORY_ORDER)).toEqual(
+        sortedKeys(prisma),
+      );
+    });
+
+    it("entries-by-category covers every Prisma category", () => {
+      const prisma = Object.values(MedicationSideEffectCategory);
+      const grouping = Object.keys(SIDE_EFFECT_ENTRIES_BY_CATEGORY);
+      expect(sortedKeys(grouping)).toEqual(sortedKeys(prisma));
+    });
+  });
+
+  describe("entry keysets", () => {
+    it("validator entries equal Prisma enum entries", () => {
+      const prisma = Object.values(MedicationSideEffectEntry);
+      expect(sortedKeys(SIDE_EFFECT_ENTRY_VALUES)).toEqual(
+        sortedKeys(prisma),
+      );
+    });
+
+    it("taxonomy SIDE_EFFECT_CATEGORIES covers every Prisma entry", () => {
+      const prisma = Object.values(MedicationSideEffectEntry);
+      const taxonomy = Object.keys(SIDE_EFFECT_CATEGORIES);
+      expect(sortedKeys(taxonomy)).toEqual(sortedKeys(prisma));
+    });
+
+    it("SIDE_EFFECT_ENTRIES_BY_CATEGORY covers every Prisma entry exactly once", () => {
+      const fromGrouping = Object.values(SIDE_EFFECT_ENTRIES_BY_CATEGORY)
+        .flat()
+        .sort();
+      const prisma = sortedKeys(Object.values(MedicationSideEffectEntry));
+      expect(fromGrouping).toEqual(prisma);
+    });
+
+    it("SIDE_EFFECT_ENTRY_COUNT matches the live Prisma enum size", () => {
+      expect(SIDE_EFFECT_ENTRY_COUNT).toBe(
+        Object.values(MedicationSideEffectEntry).length,
+      );
+    });
+  });
+
+  describe("category-for-entry agreement", () => {
+    it("every entry in SIDE_EFFECT_CATEGORIES maps to a known category", () => {
+      for (const category of Object.values(SIDE_EFFECT_CATEGORIES)) {
+        expect(Object.values(MedicationSideEffectCategory)).toContain(category);
+      }
+    });
+
+    it("grouping-side and map-side agree on every (entry, category) pair", () => {
+      for (const [category, entries] of Object.entries(
+        SIDE_EFFECT_ENTRIES_BY_CATEGORY,
+      )) {
+        for (const entry of entries) {
+          expect(SIDE_EFFECT_CATEGORIES[entry]).toBe(category);
+        }
+      }
+    });
+  });
+});
diff --git a/src/lib/medications/side-effects/validators.ts b/src/lib/medications/side-effects/validators.ts
index b5aac8af8..b7188440f 100644
--- a/src/lib/medications/side-effects/validators.ts
+++ b/src/lib/medications/side-effects/validators.ts
@@ -15,37 +15,30 @@
 
 import { z } from "zod/v4";
 
-export const SIDE_EFFECT_CATEGORY_VALUES = [
-  "GI",
-  "METABOLIC",
-  "INJECTION_SITE",
-  "COGNITIVE",
-  "GLP1_SPECIFIC",
-] as const;
+import {
+  MedicationSideEffectCategory,
+  MedicationSideEffectEntry,
+} from "@/generated/prisma/client";
 
-export const SIDE_EFFECT_ENTRY_VALUES = [
-  "NAUSEA",
-  "VOMITING",
-  "DIARRHEA",
-  "CONSTIPATION",
-  "ABDOMINAL_PAIN",
-  "HYPOGLYCEMIA_SYMPTOMS",
-  "DEHYDRATION",
-  "ANOREXIA",
-  "ELECTROLYTE_FATIGUE",
-  "INJECTION_REDNESS",
-  "INJECTION_SWELLING",
-  "INJECTION_BRUISING",
-  "INJECTION_INDURATION",
-  "BRAIN_FOG",
-  "DIZZINESS",
-  "LOW_MOOD",
-  "LOW_ENERGY",
-  "EARLY_SATIETY",
-  "GASTROPARESIS_LIKE",
-  "DYSGEUSIA",
-  "GALLBLADDER_DISCOMFORT",
-] as const;
+/**
+ * v1.4.25 W21 Fix-N (simp-M1) — these arrays used to restate the
+ * Prisma enum keys verbatim, which meant adding a new entry required
+ * three separate edits (schema, taxonomy map, validator array) that
+ * could silently drift. The arrays are now derived from the Prisma
+ * enum constant at module load. The drift-guard test
+ * (`__tests__/drift-guard.test.ts`) asserts the three sources (Prisma
+ * enum, taxonomy map, validator arrays) cover the same keys.
+ *
+ * Zod accepts the `nativeEnum` shape from the Prisma client const so
+ * the schema stays expressed in the same TypeScript-narrowable form.
+ */
+export const SIDE_EFFECT_CATEGORY_VALUES = Object.values(
+  MedicationSideEffectCategory,
+) as readonly MedicationSideEffectCategory[];
+
+export const SIDE_EFFECT_ENTRY_VALUES = Object.values(
+  MedicationSideEffectEntry,
+) as readonly MedicationSideEffectEntry[];
 
 export const SIDE_EFFECT_NOTES_MAX = 280;
 
@@ -59,7 +52,7 @@ export const SIDE_EFFECT_NOTES_MAX = 280;
  * envelope.
  */
 export const createSideEffectSchema = z.object({
-  entry: z.enum(SIDE_EFFECT_ENTRY_VALUES),
+  entry: z.nativeEnum(MedicationSideEffectEntry),
   severity: z.number().int().min(1).max(5),
   occurredAt: z.iso
     .datetime({ offset: true })