Opill 28 Day Drug Interactions: What to Avoid and What to Tell Your Doctor

Opill (norgestrel 0.075 mg) is an over-the-counter birth control pill — which means patients often start it without telling their doctor or pharmacist. That's fine for most healthy people. But it does create an important risk: Opill has significant drug interactions that can reduce its effectiveness and potentially lead to unintended pregnancy.

If you take any medications — prescription, over-the-counter, or herbal supplements — you need to know which ones can interfere with Opill before you start it. This guide covers the most important interactions clearly and practically.

Why Drug Interactions Matter More With Opill Than Combination Pills

Opill's primary mechanism of action is thickening cervical mucus — which depends on maintaining consistent norgestrel levels in your bloodstream throughout the day. This is different from combination pills, which suppress ovulation more completely.

When interacting medications speed up the breakdown of norgestrel in your body, blood levels drop — and the cervical mucus thins, potentially creating a window for sperm to reach an egg. Because Opill's protection is more dependent on consistent drug levels than combination pills are, the consequences of drug interactions can be more significant.

Major Interaction: Seizure Medications (Anticonvulsants)

This is the most important drug class to know about. Many seizure medications are potent CYP3A4 enzyme inducers — meaning they stimulate enzymes in your liver and intestine that break down drugs faster. When these enzymes are revved up, they metabolize norgestrel much more quickly than normal, causing blood levels to drop significantly.

Anticonvulsants that significantly reduce Opill's effectiveness:

Carbamazepine (Tegretol) — used for seizures, nerve pain, bipolar disorder

Phenytoin (Dilantin) — used for seizure control

Barbiturates: phenobarbital, primidone — used for seizures, migraine prevention

Oxcarbazepine (Trileptal) — used for seizures

Topiramate (Topamax) — used for seizures and migraine prevention

What to do: If you take any of these medications, do not rely on Opill as your primary contraceptive. Talk to your doctor about alternatives — a copper IUD or the Nexplanon implant (etonogestrel) are highly effective options that are not affected by CYP3A4 inducers.

Major Interaction: Rifampin and Rifabutin (Tuberculosis Treatment)

Rifampin is one of the most potent CYP3A4 inducers known. It dramatically reduces norgestrel blood levels — enough to cause contraceptive failure. The same applies to rifabutin, though to a lesser extent.

What to do: If you are treating active tuberculosis or TB exposure with rifampin, do not use Opill or any other hormonal pill as your contraceptive. Use a non-hormonal method (copper IUD or condoms) during treatment and for 28 days after stopping rifampin.

Major Interaction: Bosentan (Pulmonary Hypertension)

Bosentan (Tracleer), used to treat pulmonary arterial hypertension, is a CYP3A4 inducer that can reduce norgestrel levels and decrease Opill's effectiveness. If you take bosentan, consult your cardiologist and gynecologist about a more reliable contraceptive method.

Major Interaction: Efavirenz (HIV Medication)

Efavirenz (Sustiva), an antiretroviral medication used to treat HIV, is a CYP3A4 inducer that can reduce norgestrel concentrations. People living with HIV who are taking efavirenz should discuss alternative contraception with their healthcare provider — a long-acting method like an IUD or implant is often recommended.

Important Interaction: St. John's Wort

St. John's Wort (Hypericum perforatum) is an herbal supplement commonly used for mild depression and mood support. It contains compounds that induce CYP3A4 enzymes, which can reduce norgestrel blood levels over time.

What to do: If you take St. John's Wort regularly, consider a more reliable contraceptive method or use backup contraception consistently. Tell your pharmacist or provider about any supplements you're taking when starting Opill.

Important Interaction: Ulipristal Acetate (Ella Emergency Contraceptive)

If you have taken ella (ulipristal acetate) — an emergency contraceptive — within the past 5 days, you should NOT start Opill immediately. Progestins can interfere with ulipristal's mechanism of action, reducing the effectiveness of the emergency contraceptive. Wait at least 5 days after taking ella before starting Opill.

Conversely, if you are already taking Opill and need emergency contraception, Plan B (levonorgestrel) is preferred over ella — because ella's effectiveness is reduced by progestins.

Important Interaction: GLP-1 Medications (Weight Loss/Diabetes Drugs)

GLP-1 receptor agonists like semaglutide (Ozempic, Wegovy) and the newer orforglipron significantly delay gastric emptying — slowing the rate at which your stomach empties food and medications into the small intestine. This can reduce the absorption of oral contraceptives like Opill, potentially lowering effective norgestrel levels.

What to do: If you're starting or already taking a GLP-1 medication, use backup contraception (condoms) for at least 4 weeks after initiating GLP-1 therapy. Discuss your contraceptive options with your provider — a non-oral method may be preferable.

Interactions to Be Aware Of: Antifungals and Other Antibiotics

Griseofulvin, an antifungal medication used for fungal skin infections, may lower norgestrel levels and reduce contraceptive protection. Use backup contraception while taking griseofulvin.

Most common antibiotics (amoxicillin, doxycycline, azithromycin, etc.) do NOT significantly reduce Opill's effectiveness. The common claim that "antibiotics affect birth control" applies to rifampin, not most other antibiotics.

What to Tell Your Provider and Pharmacist

Because Opill is OTC, it may not be recorded in your medication list unless you mention it. Always tell your provider and pharmacist:

That you are taking Opill (norgestrel 0.075 mg)

About all prescription and OTC medications you take

About all herbal supplements and vitamins (especially St. John's Wort)

Before starting any new medication — ask your pharmacist if it interacts with norgestrel

For more on Opill side effects and what to watch for, see our guide on Opill side effects.