Does Benadryl cause drowiness?

Common Benadryl side effects may include:

dizziness, drowsiness, loss of coordination;

Source and more information: https://www.drugs.com/benadryl.html#side-effects

Interactions between your drugs
Moderate
diphenhydrAMINE ethanol (alcohol)
Applies to: Benadryl (diphenhydramine), Alcohol (contained in alcoholic beverages) (ethanol (alcohol))

Ask your doctor before using diphenhydrAMINE together with ethanol (alcohol). Use alcohol cautiously. Alcohol may increase drowsiness and dizziness while you are taking diphenhydrAMINE. You should be warned not to exceed recommended dosages and to avoid activities requiring mental alertness. If your doctor prescribes these medications together, you may need a dose adjustment to safely take this combination. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

Source and more information:
https://www.drugs.com/interactions-check.php?drug_list=1034-14582,896-1617