Feirza 1/20 Drug Interactions: What to Avoid and What to Tell Your Doctor

Feirza 1/20 interacts with dozens of medications — some reducing the pill's contraceptive effectiveness, others raising the risk of serious side effects. If you take any other prescription medications, supplements, or herbal products, it's essential that your healthcare provider knows you are on Feirza 1/20. This article covers the most important drug interactions to be aware of in 2026.

The Contraindicated Interaction: Hepatitis C Drugs

There is one absolute contraindication (never combine) regarding drug interactions with Feirza 1/20:

Ombitasvir/paritaprevir/ritonavir ± dasabuvir (Viekira Pak, Technivie, and related HCV combinations) — Feirza 1/20 is contraindicated with these Hepatitis C drug regimens. The combination can cause significant ALT (liver enzyme) elevations. This is listed as a contraindication in Feirza 1/20's prescribing information.

Glecaprevir/pibrentasvir (Mavyret) — Co-administration is not recommended due to potential ALT elevations.

If you are being treated for Hepatitis C, discuss alternative contraceptive methods with your provider before starting or while taking antiviral therapy.

Drugs That Reduce Feirza 1/20's Effectiveness

Several medications speed up the metabolism of the hormones in Feirza 1/20 by inducing liver enzymes (particularly CYP3A4). This lowers blood levels of norethindrone and ethinyl estradiol, potentially reducing contraceptive effectiveness and increasing breakthrough bleeding:

Rifampin (rifampicin) — The most significant inducer. Rifampin dramatically increases the metabolism of both norethindrone and ethinyl estradiol. A non-hormonal contraceptive is recommended during rifampin therapy and for 28 days after stopping it.

Anticonvulsants: phenytoin (Dilantin), phenobarbital, carbamazepine (Tegretol), oxcarbazepine (Trileptal), topiramate (Topamax), felbamate — These anti-seizure medications are CYP3A4 inducers that reduce the effectiveness of Feirza 1/20. If you take seizure medications, discuss non-hormonal or LARC contraceptive options with your provider.

St. John's Wort (Hypericum perforatum) — This herbal supplement induces CYP3A4 and p-glycoprotein, reducing the effectiveness of combination oral contraceptives. Many patients don't think of herbal products as drug interactions — this one matters significantly.

Griseofulvin (antifungal), bosentan, aprepitant, modafinil — Various other enzyme inducers that can reduce Feirza 1/20's effectiveness.

Acitretin (oral retinoid for psoriasis) — Decreases effects of norethindrone by an unknown mechanism; contraceptive failure may result.

What About Antibiotics?

You may have heard that antibiotics reduce birth control effectiveness. This is largely a myth for most antibiotics — with one important exception:

Rifampin and rifabutin — These antibiotic/antiparasitic drugs DO significantly reduce oral contraceptive effectiveness (as noted above).

Other antibiotics (amoxicillin, tetracycline, doxycycline, azithromycin, etc.) — Clinical pharmacokinetic studies have not demonstrated a consistent effect on oral contraceptive blood levels. The FDA does not currently recommend backup contraception with these antibiotics, though some clinicians advise it out of caution during short-term use.

Drugs Affected BY Feirza 1/20 (Feirza Changes Their Blood Levels)

The estrogen in Feirza 1/20 can also affect how your body processes other medications:

Lamotrigine (Lamictal) — seizure medication — Ethinyl estradiol increases glucuronidation of lamotrigine, significantly reducing its blood levels. This can reduce seizure control. Patients on lamotrigine and Feirza 1/20 require close monitoring and may need lamotrigine dose adjustments.

Cyclosporine, theophylline, voriconazole, tizanidine — COCs containing ethinyl estradiol may inhibit the metabolism of these drugs, increasing their plasma concentrations and potential toxicity.

Acetaminophen, clofibric acid, morphine, salicylic acid, temazepam — COCs have been shown to decrease plasma concentrations of these drugs, potentially reducing their effectiveness.

Tranexamic acid (oral) — Contraindicated with combination hormonal contraceptives because of significantly increased thrombotic risk through pharmacodynamic synergism.

Supplements and Food Interactions

Beyond St. John's Wort, be aware of:

Vitamin C and acetaminophen — May increase ethinyl estradiol levels by inhibiting its conjugation (breakdown). Clinically, this is unlikely to be significant at typical supplement doses.

Grapefruit juice — Not a significant interaction with norethindrone acetate/ethinyl estradiol at this dose, unlike some other medications.

What to Tell Your Doctor and Pharmacist

When starting Feirza 1/20 (or any new prescription), make sure your prescriber and pharmacist know about:

All prescription medications (especially anticonvulsants, HIV antivirals, antifungals, antibiotics)

All over-the-counter drugs (including acetaminophen, ibuprofen, antacids)

All herbal supplements and natural products (especially St. John's Wort)

Any planned surgeries or extended bed rest periods — COCs may need to be paused before major surgery due to clot risk

The Bottom Line

Feirza 1/20 has significant interactions with enzyme inducers (rifampin, anticonvulsants, St. John's Wort), certain HCV antivirals (absolute contraindication), and can affect other drugs including lamotrigine. Always disclose all medications and supplements to your prescriber and pharmacist. For more on side effects to watch for, see our article on Feirza 1/20 side effects. If you need help finding Feirza 1/20 at a pharmacy, medfinder can check nearby pharmacies on your behalf.