Unable to sleep is not a side effect of anastrolzole. It might be due to other unknown reason or due to old ageing. Benadryl is not used for sleep induction although it has a sedative effect. Other more safer and effective treatment for sleep induction is available but none is over the counter for sell. Those include alprazolam or zolpidem. As you have problem in staying asleep, so alprazolam is a better choice for you. You can discuss with your doctor. Advice 1. Continue anastrozole as suggested 2. Alprazolam at bed time per oral for 30 days 3. Do not use alprazolam for more than 30 days as it is addicting 4. Avoid Benadryl 5. Avoid driving & swimming because it may impair ability to drive or operate machinery while on alprazolam or Benadryl 6. Stop smoking, alcohol and coffee specially at night as it might impair your sleep 7. Try to have time for exercise. Start workout at least half an hour in a day for 5 days in a week. It will induce sleep 8. Stop work till late night I hope this information will help you. I will be happy if you ask another question Thank