Levonorgestrel Interactions: What You Need to Know Before Taking It

When you take levonorgestrel, a synthetic hormone used in birth control pills and emergency contraception. It's known by brand names like Plan B, Skyla, and Mirena, and it works by stopping ovulation or preventing fertilization. But what you might not realize is that other things you take — medicines, herbs, even some foods — can interfere with how levonorgestrel works in your body.

Some antibiotics, like rifampin used for tuberculosis, can make levonorgestrel less effective by speeding up how fast your liver breaks it down. The same goes for certain seizure medications, such as phenytoin or carbamazepine. Even St. John’s wort, a popular herbal supplement for mood, is known to reduce hormone levels. If you’re on any of these, your birth control might not work as it should — and that means a higher chance of pregnancy.

It’s not just about effectiveness. Some drugs can make side effects worse. If you’re taking liver-metabolized drugs, like certain antidepressants or cholesterol meds, levonorgestrel can compete for the same enzymes, leading to higher levels of either drug in your blood. That could mean more nausea, headaches, or mood swings. And if you’re already prone to blood clots, mixing levonorgestrel with other hormone-based treatments — like thyroid meds or corticosteroids — can raise your risk.

You don’t need to stop your meds, but you do need to talk to your doctor or pharmacist before starting levonorgestrel. Keep a list of everything you take — even over-the-counter painkillers or sleep aids. Some people think emergency contraception is safe to use anytime, but if you’ve been on rifampin for weeks, that one pill might not be enough. You might need a higher dose or a different method altogether.

And here’s something most people miss: interactions don’t always show up right away. If you’ve been taking a seizure drug for months and then start levonorgestrel, the problem might not hit until weeks later. That’s why tracking your cycle and symptoms matters. Missed periods, breakthrough bleeding, or unusual fatigue could be signs your body isn’t processing the hormone properly.

What you’ll find below are real, practical guides from people who’ve been there — whether it’s how to safely use levonorgestrel with other meds, what to do if you accidentally took it with an interaction, or how to spot early warning signs. These aren’t theory pieces. They’re lived experiences, backed by clinical data, and written for anyone who’s tired of guessing whether their birth control is really working.