Does Lamotrigine affect birth control effectiveness?

Question

Hello doctor,

I had sex with my boyfriend yesterday, which stated I had 14 more days before my next period. I take a birth control pill (Junel Fe 1.5/30) every day and usually take it when I wake up. The time of day changes depending on when I wake up, but I try to keep the timing close. Yesterday, I had sex, but I am also on a medication (Lamotrigine) that affects my birth control brand and lowers its effectiveness.

Should I be worried about being pregnant?

Please help.

Thank you.

Answer 1

Hi,

Welcome to icliniq.com.

I have gone through your query and understand your concern.

Since Lamotrigine (an anti-seizure drug) can lower the effectiveness of combined birth control pills (like Junel Fe 1.5/30), there is a slightly increased risk of pregnancy, but not a guaranteed failure.

Factors to consider:

You are taking the pill daily – This reduces pregnancy risk, even if the timing varies slightly.
You are mid-cycle (ovulation window) – If Lamotrigine reduces your pill’s effectiveness, there is a higher chance of ovulation, which increases pregnancy risk.
No backup contraception used – Since Lamotrigine weakens birth control, a backup method (like condoms) is usually recommended.

Should you take emergency contraception?

If you are very concerned, taking Plan B (Levonorgestrel) within 72 hours can lower the risk of pregnancy.
If you are under 155 lbs (70 kg), Plan B works well.
If you are over 155 lbs, consider Ella (Ulipristal acetate) instead, as it is more effective for higher weights.

What you should do next:

Consider emergency contraception as soon as possible if you are worried.
Use backup protection (condoms) in the future while on Lamotrigine.
Take a pregnancy test if your period is late or abnormal.

Would you like recommendations for a birth control method that works better with Lamotrigine?

I hope I have answered your question.

Let me know if I can assist you further.

Thank you.