Is it dangerous to take doxycycline and plan b at the same time?

No: I didn't find any interaction between Doxycycline ; Plan B at http://www.Drugs.Com/interactions-check.Php?Drug_list=940-0, 1461-13923. As always, tell your prescribing doctor ; dispensing pharmacist everything you're taking, both prescription ; otc, so they can look for interactions.

Agree w Dr Lin: No interaction with Plan B and doxycycline. Antibiotics which can affect Plan B: ampicillin, cotrimoxazole (in Bactrim), Rifampin, tetracycline, & clarithromycin.