diff --git a/app/auth.py b/app/auth.py
index 199943a..07348e1 100644
--- a/app/auth.py
+++ b/app/auth.py
@@ -1,14 +1,28 @@
+import time
 from fastapi import HTTPException
 from twilio.rest import Client
 from app.config import TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN, TWILIO_VERIFY_SERVICE_SID
 
 client = Client(TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN)
 
+last_otp_times = {}
+COOLDOWN_PERIOD = 30
+
 def send_otp(phone: str):
+    current_time = time.time()
+    last_sent_time = last_otp_times.get(phone)
+    if last_sent_time and current_time - last_sent_time < COOLDOWN_PERIOD:
+        wait_time = int(COOLDOWN_PERIOD - (current_time - last_sent_time))
+        raise HTTPException(
+            status_code=429,
+            detail=f"OTP already sent. Please wait {wait_time} more seconds before retrying."
+        )
+    
     try:
         verification = client.verify.services(TWILIO_VERIFY_SERVICE_SID).verifications.create(
             to=phone, channel="sms"
         )
+        last_otp_times[phone] = current_time
         return {"status": verification.status}
     except Exception as e:
         raise HTTPException(status_code=500, detail=str(e))