diff --git a/src/__tests__/api/doubts-check-duplicate.test.ts b/src/__tests__/api/doubts-check-duplicate.test.ts
index 0c054a91..039b1228 100644
--- a/src/__tests__/api/doubts-check-duplicate.test.ts
+++ b/src/__tests__/api/doubts-check-duplicate.test.ts
@@ -133,6 +133,42 @@ describe("Doubt check-duplicate API endpoint", () => {
     await expect(res.json()).resolves.toMatchObject({ error: "Unauthorized" });
   });
 
+  it("excludes hidden doubts from candidate query", async () => {
+    let capturedWhereArg: any = null;
+    const trackingQuery: any = {
+      from: () => trackingQuery,
+      where: (arg: any) => {
+        capturedWhereArg = arg;
+        return trackingQuery;
+      },
+      orderBy: () => trackingQuery,
+      limit: () => trackingQuery,
+      then: (resolve: any) => Promise.resolve(resolve([])),
+    };
+    dbSelectMock.mockReturnValue(trackingQuery);
+
+    const req = new Request("http://localhost/api/doubts/check-duplicate", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({
+        content: "How does photosynthesis convert light into energy?",
+      }),
+    });
+
+    const res = await POST(req);
+
+    expect(res.status).toBe(200);
+    expect(capturedWhereArg).not.toBeNull();
+    const hasIsHidden = (expr: any): boolean => {
+      if (!expr || typeof expr !== "object") return false;
+      if (expr.name === "isHidden") return true;
+      if (expr.queryChunks)
+        return expr.queryChunks.some((c: any) => hasIsHidden(c));
+      return false;
+    };
+    expect(hasIsHidden(capturedWhereArg)).toBe(true);
+  });
+
   it("succeeds for authenticated classroom duplicate checks", async () => {
     const requireMembershipMock = requireMembership as jest.MockedFunction<typeof requireMembership>;
     requireMembershipMock.mockResolvedValue({ role: "student" });
diff --git a/src/__tests__/api/doubts-similarity.test.ts b/src/__tests__/api/doubts-similarity.test.ts
index 06cbe880..12822d8d 100644
--- a/src/__tests__/api/doubts-similarity.test.ts
+++ b/src/__tests__/api/doubts-similarity.test.ts
@@ -1,3 +1,18 @@
+process.env.GROQ_API_KEY = "mock-groq-key";
+
+jest.mock("@/lib/ai/groq-client", () => ({
+  groq: {
+    embeddings: {
+      create: jest.fn(),
+    },
+    chat: {
+      completions: {
+        create: jest.fn(),
+      },
+    },
+  },
+}));
+
 import { currentUser } from "@clerk/nextjs/server";
 import { NextResponse } from "next/server";
 
@@ -170,6 +185,42 @@ describe("Doubt similarity API endpoint", () => {
     });
   });
 
+  it("excludes hidden doubts from candidate query", async () => {
+    let capturedWhereArg: any = null;
+    const trackingQuery: any = {
+      from: () => trackingQuery,
+      where: (arg: any) => {
+        capturedWhereArg = arg;
+        return trackingQuery;
+      },
+      orderBy: () => trackingQuery,
+      limit: () => trackingQuery,
+      then: (resolve: any) => Promise.resolve(resolve([])),
+    };
+    dbSelectMock.mockReturnValue(trackingQuery);
+
+    const req = new Request("http://localhost/api/doubts/check-similarity", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({
+        content: "How does photosynthesis convert light into energy?",
+      }),
+    });
+
+    const res = await POST(req);
+
+    expect(res.status).toBe(200);
+    expect(capturedWhereArg).not.toBeNull();
+    const hasIsHidden = (expr: any): boolean => {
+      if (!expr || typeof expr !== "object") return false;
+      if (expr.name === "isHidden") return true;
+      if (expr.queryChunks)
+        return expr.queryChunks.some((c: any) => hasIsHidden(c));
+      return false;
+    };
+    expect(hasIsHidden(capturedWhereArg)).toBe(true);
+  });
+
   it("requires authentication for classroom similarity checks", async () => {
     const req = new Request("http://localhost/api/doubts/check-similarity", {
       method: "POST",
diff --git a/src/__tests__/lib/embeddings.test.ts b/src/__tests__/lib/embeddings.test.ts
index d209a6bd..e035761a 100644
--- a/src/__tests__/lib/embeddings.test.ts
+++ b/src/__tests__/lib/embeddings.test.ts
@@ -56,4 +56,33 @@ describe("Embeddings & Vector Duplicate Utilities", () => {
     const duplicates = await findSemanticDuplicates({ content: "What is momentum?" });
     expect(duplicates).toEqual([]);
   });
+
+  it("findSemanticDuplicates excludes hidden doubts from candidate query", async () => {
+    const mockVector = new Array(1536).fill(0.1);
+    (groq.embeddings.create as jest.Mock).mockResolvedValueOnce({
+      data: [{ embedding: mockVector }],
+    });
+
+    const selectMock = db.select as jest.Mock;
+    const whereMock = jest.fn().mockReturnThis();
+    selectMock.mockReturnValue({
+      from: jest.fn().mockReturnThis(),
+      where: whereMock,
+      orderBy: jest.fn().mockReturnThis(),
+      limit: jest.fn().mockResolvedValue([]),
+    });
+
+    await findSemanticDuplicates({ content: "What is momentum?" });
+
+    expect(whereMock).toHaveBeenCalledTimes(1);
+    const whereArg = whereMock.mock.calls[0][0];
+    const hasIsHidden = (expr: any): boolean => {
+      if (!expr || typeof expr !== "object") return false;
+      if (expr.name === "isHidden") return true;
+      if (expr.queryChunks)
+        return expr.queryChunks.some((c: any) => hasIsHidden(c));
+      return false;
+    };
+    expect(hasIsHidden(whereArg)).toBe(true);
+  });
 });
diff --git a/src/app/api/doubts/check-duplicate/route.ts b/src/app/api/doubts/check-duplicate/route.ts
index eff6c02b..22385ac2 100644
--- a/src/app/api/doubts/check-duplicate/route.ts
+++ b/src/app/api/doubts/check-duplicate/route.ts
@@ -95,6 +95,7 @@ export async function POST(req: Request) {
             : isNull(doubtsTable.classroomId),
           eq(doubtsTable.type, "community"),
           isNull(doubtsTable.deletedAt),
+          eq(doubtsTable.isHidden, false),
         ),
       )
       .orderBy(desc(doubtsTable.createdAt))
diff --git a/src/app/api/doubts/check-similarity/route.ts b/src/app/api/doubts/check-similarity/route.ts
index f1fffd61..69f76afb 100644
--- a/src/app/api/doubts/check-similarity/route.ts
+++ b/src/app/api/doubts/check-similarity/route.ts
@@ -102,6 +102,7 @@ export async function POST(req: Request) {
             : isNull(doubtsTable.classroomId),
           eq(doubtsTable.type, "community"),
           isNull(doubtsTable.deletedAt),
+          eq(doubtsTable.isHidden, false),
         ),
       )
       .orderBy(desc(doubtsTable.createdAt))
diff --git a/src/lib/ai/embeddings.ts b/src/lib/ai/embeddings.ts
index 1c068007..309b524a 100644
--- a/src/lib/ai/embeddings.ts
+++ b/src/lib/ai/embeddings.ts
@@ -104,6 +104,7 @@ export async function findSemanticDuplicates(params: {
       : isNull(doubtsTable.classroomId),
     eq(doubtsTable.type, type),
     isNull(doubtsTable.deletedAt),
+    eq(doubtsTable.isHidden, false),
     // exclude null embeddings
     sql`${doubtsTable.embedding} IS NOT NULL`,
   );