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

Amethyst 28 Day (levonorgestrel 90 mcg / ethinyl estradiol 20 mcg) can interact with several medications and supplements, potentially reducing its contraceptive effectiveness or increasing side effect risk. Here's what you need to know — and what to tell your doctor and pharmacist.

Drugs That Can Reduce Amethyst 28 Day's Effectiveness

The following medications can make Amethyst 28 Day less effective at preventing pregnancy by increasing the speed at which your body metabolizes the hormones (via liver enzyme induction):

Seizure Medications (Anticonvulsants)

Carbamazepine (Tegretol, Carbatrol): A strong inducer of CYP3A4 enzymes; significantly reduces hormone levels in the blood. Use backup contraception for at least 28 days after stopping carbamazepine.

Phenytoin (Dilantin): Another strong CYP inducer that can significantly reduce Amethyst 28 Day's effectiveness.

Felbamate, oxcarbazepine, topiramate (Topamax), phenobarbital: All can reduce oral contraceptive effectiveness. Discuss alternative contraception with your provider if you take any of these.

HIV Medications (Antiretrovirals)

Many HIV antiretroviral medications can decrease the effectiveness of hormonal contraceptives through enzyme induction or inhibition. Ritonavir-boosted regimens are of particular concern. If you're on HIV treatment, consult your HIV specialist and prescriber to choose the safest contraceptive option.

Hepatitis C Medications

Viekira Pak (dasabuvir / ombitasvir / paritaprevir / ritonavir): This combination is CONTRAINDICATED with Amethyst 28 Day. Taking them together can cause significant liver enzyme elevations (ALT increases). Amethyst 28 Day must be stopped before starting Viekira Pak and may be resumed 2 weeks after the Viekira Pak regimen ends.

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Antibiotics

The concern about antibiotics and oral contraceptives has been a long-standing one — but the evidence has largely shifted. Most commonly prescribed antibiotics (amoxicillin, azithromycin, doxycycline, metronidazole) do NOT reliably reduce combination oral contraceptive effectiveness for most patients, according to current evidence.

The notable exception is rifampin/rifampicin (used for tuberculosis and certain other infections), which is a potent CYP3A4 inducer and does significantly reduce OC effectiveness. Use backup contraception if taking rifampin and for at least 28 days after stopping it.

St. John's Wort (Herbal Supplement)

St. John's Wort (Hypericum perforatum) is a popular herbal supplement used for depression and anxiety. It is a known inducer of CYP450 enzymes and P-glycoprotein, and it can significantly reduce the blood levels of levonorgestrel and ethinyl estradiol — potentially to the point of contraceptive failure. It may also cause breakthrough bleeding.

Avoid St. John's Wort while taking Amethyst 28 Day, or use a reliable backup method of contraception if you continue to use it.

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Drugs That Amethyst 28 Day Can Affect

Amethyst 28 Day can also affect the levels or effectiveness of other medications:

Lamotrigine (Lamictal): Combination oral contraceptives can significantly decrease lamotrigine serum levels, potentially reducing seizure control. This is an important interaction for patients with epilepsy. Work closely with your neurologist if you're on lamotrigine and starting Amethyst 28 Day.

Warfarin (Coumadin): Oral contraceptives may alter the effect of warfarin (increase or decrease anticoagulation). INR monitoring is recommended when starting or stopping Amethyst 28 Day in warfarin-treated patients.

Thyroid medications: Estrogen can increase thyroid-binding globulin (TBG), which may require adjustment in thyroid medication dosing for patients with hypothyroidism.

Atorvastatin (Lipitor): Atorvastatin can increase ethinyl estradiol AUC by about 20%, potentially increasing estrogen side effects. Clinical significance is generally low.

What to Tell Your Doctor and Pharmacist

Before starting or continuing Amethyst 28 Day, tell your provider about every medication you take — including:

All prescription medications (especially seizure drugs, HIV medications, and blood thinners)

Over-the-counter drugs (including antifungals, antacids, and pain relievers)

Vitamins and supplements (especially St. John's Wort, vitamin C in high doses)

Any herbal teas or products (some contain St. John's Wort in unlisted forms)

If an interacting medication causes Amethyst 28 Day to fail as a contraceptive, there may be no warning signs — which is why proactive communication with your provider matters. Read our guide on Amethyst 28 Day side effects for more on how to manage your medication safely.