What happens if I take two medicines both containing diphenhydramine?

Too much Benadryl (diphenhydramine) You should read how much Benadryl (diphenhydramine) is in each one. If you only take it in therapeutic doses you will mostl likely be ok, but will feel drowsy and sometimes hypotensive. You should ask your docotr if you should take the two meds together, that is hte best answer.