Updated: January 22, 2026

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

Author

Peter Daggett

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How Dutasteride Is Metabolized — The CYP3A4 Connection
Drugs That Increase Dutasteride Levels (CYP3A4 Inhibitors)
Drugs That Decrease Dutasteride Levels (CYP3A4 Inducers)
Food and Supplement Interactions
Combination Products: Dutasteride + Tamsulosin (Jalyn)
What to Tell Your Doctor Before Starting Dutasteride
The Bottom Line

Dutasteride is metabolized by CYP3A4, so CYP3A4 inhibitors can raise its levels. Here's a complete guide to dutasteride drug interactions and what to tell your doctor.

Dutasteride has a relatively modest drug interaction profile compared to many other medications, but important interactions do exist — particularly with drugs that affect CYP3A4 liver enzymes. This guide covers what you need to know about dutasteride drug interactions, what to avoid, and what to tell your doctor and pharmacist before starting.

How Dutasteride Is Metabolized — The CYP3A4 Connection

Dutasteride is primarily metabolized in the liver by the CYP3A4 enzyme (and to a lesser extent, CYP3A5). This is the key to understanding dutasteride's drug interaction profile. Any medication, food, or supplement that affects CYP3A4 activity has the potential to change how much dutasteride is in your bloodstream:

CYP3A4 inhibitors slow down dutasteride metabolism → higher dutasteride blood levels → increased risk of side effects.

CYP3A4 inducers speed up dutasteride metabolism → lower dutasteride blood levels → reduced effectiveness.

Drugs That Increase Dutasteride Levels (CYP3A4 Inhibitors)

These medications can increase dutasteride blood concentrations, potentially increasing the risk of side effects like decreased libido and erectile dysfunction:

Antifungals: Ketoconazole, itraconazole, fluconazole, voriconazole, levoketoconazole. These are potent to moderate CYP3A4 inhibitors. Use with caution and monitor for increased dutasteride side effects.

Antibiotics: Clarithromycin (Biaxin), erythromycin. Ciprofloxacin is also a moderate CYP3A4 inhibitor.

HIV/AIDS medications: Ritonavir (Norvir) and other protease inhibitors are strong CYP3A4 inhibitors. Can significantly raise dutasteride levels.

Calcium channel blockers: Diltiazem (Cardizem) and verapamil (Calan) are moderate CYP3A4 inhibitors. May modestly increase dutasteride levels.

Antidepressants: Nefazodone is a strong CYP3A4 inhibitor.

Isoniazid (INH): Used for tuberculosis; inhibits CYP3A4.

Cimetidine (Tagamet): This OTC antacid medication is a CYP enzyme inhibitor and can increase dutasteride levels. Notably, it's an over-the-counter product that patients may not think to mention to their doctor.

Drugs That Decrease Dutasteride Levels (CYP3A4 Inducers)

These medications speed up dutasteride metabolism, potentially reducing its effectiveness:

Carbamazepine (Tegretol): Seizure and mood disorder medication; strong CYP3A4 inducer.

Rifampin (Rifadin): Antibiotic used for tuberculosis; very strong CYP3A4 inducer.

Rifabutin: Similar to rifampin; moderate CYP3A4 inducer.

Primidone (Mysoline): Seizure medication; increases breakdown of dutasteride.

Food and Supplement Interactions

Grapefruit and grapefruit juice: Grapefruit contains furanocoumarins that inhibit intestinal CYP3A4, which can raise dutasteride blood levels. Your doctor may recommend limiting grapefruit while on dutasteride.

St. John's Wort: This popular herbal supplement is a CYP3A4 inducer and can significantly lower dutasteride blood levels, potentially reducing its effectiveness. Avoid taking St. John's Wort while on dutasteride unless your prescriber approves.

Combination Products: Dutasteride + Tamsulosin (Jalyn)

Dutasteride is FDA-approved in combination with tamsulosin (Flomax) as the product Jalyn for BPH. This combination is generally well-tolerated. However, tamsulosin (an alpha-blocker) can cause a significant drop in blood pressure, especially orthostatic hypotension (dizziness upon standing). Taking other antihypertensives, PDE5 inhibitors (like tadalafil or sildenafil), or other alpha-blockers alongside Jalyn increases this risk. Tell your doctor about all blood pressure medications you take.

What to Tell Your Doctor Before Starting Dutasteride

Always give your prescriber and pharmacist a complete medication list before starting dutasteride. Be sure to mention:

All prescription medications, including heart, blood pressure, seizure, antifungal, antibiotic, HIV, and antidepressant drugs.

OTC medications, especially cimetidine (Tagamet).

Herbal supplements, especially St. John's Wort.

Liver disease or liver problems — dutasteride is metabolized by the liver.

The Bottom Line

Dutasteride has a manageable drug interaction profile centered on CYP3A4. Be particularly watchful with antifungals, certain antibiotics, HIV medications, cimetidine, and St. John's Wort. For a related guide, read about dutasteride side effects and what to expect. And if you need help finding dutasteride in stock near you, medfinder is here to help.

Frequently Asked Questions

The most important drugs to watch out for are CYP3A4 inhibitors, which increase dutasteride blood levels. These include antifungals (ketoconazole, itraconazole, fluconazole), antibiotics (clarithromycin, erythromycin), HIV medications (ritonavir), calcium channel blockers (diltiazem, verapamil), and the OTC antacid cimetidine. Also avoid St. John's Wort (a CYP3A4 inducer that reduces dutasteride effectiveness).

Yes — dutasteride and tamsulosin are actually available together as an FDA-approved combination product called Jalyn. Combining them provides complementary benefits for BPH: dutasteride shrinks the prostate over months, while tamsulosin quickly relaxes muscle tissue for faster urinary symptom relief. The main caution is that tamsulosin can cause blood pressure to drop (especially when standing up), which is worsened by other blood pressure medications or erectile dysfunction drugs.

Yes. Grapefruit and grapefruit juice contain compounds that inhibit intestinal CYP3A4 enzymes, which can increase dutasteride blood levels. Your doctor may advise you to limit or avoid grapefruit while taking dutasteride. This interaction is typically minor, but it's worth discussing with your prescriber, especially if you eat grapefruit regularly.

Cimetidine (Tagamet), an over-the-counter heartburn medication, is a CYP enzyme inhibitor that can increase dutasteride plasma concentrations. While the interaction is not typically considered severe, you should inform your prescriber or pharmacist if you use cimetidine regularly while taking dutasteride. Omeprazole, famotidine, or other acid reducers are generally preferred as they do not have this interaction.

Yes. St. John's Wort is a CYP3A4 inducer — it speeds up the breakdown of dutasteride in the liver, potentially lowering its blood levels and reducing its effectiveness. If you take St. John's Wort for mood or other reasons, inform your prescriber before starting dutasteride. Your doctor may recommend discontinuing the supplement or adjusting your medication plan accordingly.

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