Menest Drug Interactions: What to Avoid and What to Tell Your Doctor

Menest (esterified estrogens) interacts with more than 250 known medications, including 33 major interactions. Before starting Menest, make sure your doctor and pharmacist know about every medication, supplement, and herbal product you take. This guide covers the most clinically significant interactions.

Why Does Menest Interact With So Many Drugs?

Menest is metabolized (broken down) in the liver by two enzyme systems: CYP3A4 and CYP1A2. Many common medications either speed up these enzymes (causing Menest to be eliminated faster, reducing its effectiveness) or slow them down (causing Menest levels to build up in the blood, increasing side effect risk). Understanding these interactions helps you and your healthcare team manage your therapy safely.

Contraindicated: Do Not Combine With Menest

These drug combinations should be avoided:

Ospemifene (Osphena) — combining ospemifene with estrogens creates additive estrogenic effects that can increase risk of endometrial cancer and other estrogen-related harms. Contraindicated.

Anastrozole (Arimidex) and Exemestane — Menest reduces the effectiveness of these aromatase inhibitors, which are used to treat estrogen receptor-positive breast cancer. Combining them is counterproductive. Contraindicated.

Antithrombin alfa — Menest can reduce the effectiveness of this blood thinner by increasing clotting risk. Contraindicated.

Drugs That REDUCE Menest Levels (May Make It Less Effective)

These drugs speed up the liver enzymes that break down Menest, reducing blood levels and potentially making it less effective at controlling your symptoms:

Rifampin (antibiotic) — one of the most potent CYP3A4 inducers; can significantly reduce Menest levels

Barbiturates (phenobarbital, primidone) — seizure medications that induce liver enzymes

Carbamazepine (Tegretol) — seizure and mood stabilizer; induces CYP3A4

Phenytoin (Dilantin) — anti-seizure medication; induces CYP3A4

Griseofulvin — antifungal that induces CYP3A4

St. John's Wort — popular herbal supplement that induces CYP3A4; a very common cause of herb-drug interactions. If you take St. John's Wort for mood, tell your doctor before starting Menest.

Lorlatinib, Apalutamide, Enzalutamide, Ivosidenib — cancer medications that strongly induce CYP3A4; may require alternative estrogen or dose adjustment

Drugs That INCREASE Menest Levels (May Increase Side Effects)

These drugs slow the liver enzymes that break down Menest, causing it to accumulate to higher levels in the blood — potentially increasing side effects:

Erythromycin (multiple formulations) — common antibiotic; inhibits CYP3A4

Ketoconazole and Itraconazole — antifungals; potent CYP3A4 inhibitors

Ritonavir and Lopinavir — HIV antiretrovirals; potent CYP3A4 inhibitors

Idelalisib, Tucatinib, Fexinidazole — cancer/antiparasitic medications that inhibit CYP3A4

Grapefruit juice — inhibits intestinal CYP3A4, increasing estrogen absorption. Regularly drinking large amounts of grapefruit juice may raise Menest levels and side effects.

Other Important Interactions to Discuss With Your Doctor

Warfarin (blood thinner) — Menest increases the liver's production of clotting proteins, which can counteract warfarin. Monitor INR closely if starting or stopping Menest while on warfarin.

Thyroid medications (levothyroxine) — oral estrogens increase thyroxine-binding globulin, which may raise the dose of thyroid medication needed to maintain proper thyroid levels.

Insulin and diabetes medications — estrogens can affect glucose tolerance; blood sugar may need closer monitoring when starting or changing Menest.

Growth hormone medications (lonapegsomatropin, somapacitan) — oral estrogens can reduce the IGF-1 response to growth hormone therapy; higher doses of growth hormone medications may be needed.

What to Tell Your Doctor and Pharmacist

Before starting Menest, give your doctor and pharmacist a complete list of:

All prescription medications (especially seizure meds, antibiotics, HIV medications, cancer treatments)

Over-the-counter medications (including aspirin, ibuprofen, antacids)

Vitamins and mineral supplements

Herbal products, especially St. John's Wort, black cohosh, soy supplements

For a full guide to Menest side effects, see: Menest Side Effects: What to Expect and When to Call Your Doctor.

If you're having trouble filling your Menest prescription, medfinder can locate a pharmacy near you that has it in stock.