How often can I take benedryl, for allergies every what hours if 7 months pregnant?

Four. Diphenhydramine (generic of benadryl) 25 mg, 1 tab, every 4 hours, is the usual starting dose. If you are not controlled and not sedated you can increase to 2 tabs every 4 hours. A better alternative is Cetirizine 10 mg, 1 tab, once day. Studies show Cetirizine 10 mg, once a day is therapeutically equivalent to Diphenhydramine 25 mg, 3-4x/day with much less, if any, sedation.