Plan B and Antibiotics


Q: Does Cephalexin counteract the plan B pill? just wondering because my girlfriend is on Cephalexin and is worried. thanks for anything that you can tell me


A:   That is a very good question David.
There are some antibiotics that do interact with certain oral birth controls.
Cephelexin is in the group of broad-spectrum antibiotics called cephalosporins. Some broad-spectrum antibiotics may reduce the efficacy of combined (progesterone + estrogen) oral contraceptives by impairing bacterial flora responsible for recycling of estrogen in the large intestine. Therefore, the drug tends to be removed from the system more quickly and reduces the effectiveness of the birth control.
However, Plan B is in a category by itself since it is only taken for 2 doses and the main purpose is emergency contraception.  Cephelexin has a low percentage of interacting with Plan B but as a precautionary measure you  should be using a second form of contraception (i.e condoms, spermicidal agents) for 7 days.  Hope this helps you both.

Related Q&A

Q: I take the Lutera birth control pill everyday at 11pm. Last night (Saturday) I took a pill at 11pm and this morning (...

Q: Hi - I'm on Alesse for birth control and since having our daughter 7 months ago, I'm quite religious with my pill but...

Q: I have had bilateral PE, DVT x2 and clot behind my eye in the past. My doctor was away and a new doctor put in the im...

Q: I have taken an i-pill on 31st October, my periods was due on 18 but I got it on 7th. But the bleeding is very low wi...

Q: I hVe taken two extra days worth of levlen ed for birth control by mistake and just wanted to no if i should wait two...


Dr. James Obaji M.D.

  • 247 Reviews
  • Family Physician

Dr. Suneel Sharman M.D.

  • 190 Reviews
  • Family Physician

Dr. Pat Golden M.D.

  • 169 Reviews
  • Cardiologist

Dr. Kunaal Jindal M.D.

  • 112 Reviews
  • Plastic Surgeon