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

Incassia 28 Day (norethindrone 0.35 mg) can interact with certain medications, supplements, and substances — primarily by reducing its effectiveness as a contraceptive. Because this is a progestin-only pill with a strict 3-hour timing requirement and only partial ovulation suppression, any reduction in norethindrone's blood levels can meaningfully increase the risk of unintended pregnancy.

Always tell your doctor, nurse practitioner, and pharmacist about every medication, supplement, and herbal product you take — including over-the-counter items.

Drugs That Reduce Incassia's Effectiveness (Major Interactions)

These medications work by inducing liver enzymes (primarily CYP3A4) that break down norethindrone more rapidly, reducing its concentration in your blood:

Anticonvulsants / Anti-Seizure Medications

Rifampin (rifampicin) — An antibiotic primarily used for tuberculosis; one of the most potent reducers of hormonal contraceptive levels.

Phenobarbital, primidone — Barbiturate anticonvulsants; significantly reduce norethindrone blood levels.

Carbamazepine (Tegretol) — Anti-seizure medication; induces liver enzymes that metabolize norethindrone faster.

Phenytoin (Dilantin) — Anti-seizure medication; similar enzyme-inducing effect.

Topiramate (Topamax) — Used for seizures and migraines; may reduce hormonal contraceptive efficacy, especially at higher doses.

Anti-HIV Medications (Some)

Ritonavir, lopinavir, nelfinavir — Protease inhibitors used in HIV treatment; may alter norethindrone metabolism. Consult your HIV specialist about the best contraceptive choice.

Emergency Contraceptives

Ulipristal (Ella, Logilia) — This emergency contraceptive works as a progesterone receptor modulator and may counteract norethindrone's effects. If you take ulipristal, restart Incassia immediately after but use backup contraception for 7 days.

Herbal Supplements

St. John's Wort (Hypericum perforatum) — This widely used herbal supplement for depression is one of the most significant reducers of hormonal contraceptive effectiveness. St. John's Wort is a potent inducer of liver enzymes that break down norethindrone. Do not take it while using Incassia without discussing an alternative contraceptive method with your provider.

Antifungals

Griseofulvin — An antifungal used for skin and nail fungal infections; may reduce hormonal contraceptive effectiveness. Use backup contraception during treatment.

What About Antibiotics?

The old advice to use backup contraception with all antibiotics has been revised. Current evidence shows that most common antibiotics (amoxicillin, azithromycin, doxycycline, etc.) do NOT meaningfully reduce norethindrone effectiveness. The main exception is rifampin, which is used specifically for tuberculosis and is in a different category.

However, if an antibiotic causes severe diarrhea or vomiting, absorption of norethindrone may be reduced. Use backup contraception if this occurs.

Does Incassia Interact With Other Medications You May Be Taking?

In addition to other drugs affecting norethindrone, norethindrone can also affect the levels of other medications in your body. Examples:

Diabetes medications: Progestins can mildly affect glucose tolerance. Diabetic patients should monitor blood sugar levels more closely when starting Incassia.

Thyroid medications: Hormonal contraceptives can alter thyroid hormone binding. Patients on thyroid medication may need dose adjustments — check with your provider.

Things to Avoid or Be Cautious About

Smoking: While norethindrone doesn't carry the cardiovascular risks of estrogen-containing pills, smoking is still discouraged for overall cardiovascular health.

Bariatric surgery: Malabsorption following certain bariatric procedures may reduce norethindrone absorption and effectiveness. Discuss alternative contraception with your bariatric surgeon and OB/GYN.

What to Tell Your Doctor and Pharmacist

Before starting Incassia, provide a full list of:

All prescription medications

Over-the-counter medications (including pain relievers, antacids, vitamins)

Herbal supplements (especially St. John's Wort, valerian, ginseng)

Any history of seizures, HIV treatment, or tuberculosis treatment

Related: Incassia 28 Day Side Effects: What to Expect and When to Call Your Doctor.