5-alpha-reductase inhibitor (5-ARI)

Why blocking DHT matters

DHT is the androgen most responsible for two common midlife problems in men. In the scalp, it gradually shrinks genetically sensitive hair follicles, causing male pattern hair loss. In the prostate, it drives the slow, noncancerous growth known as benign prostatic hyperplasia (BPH), which can weaken the urine stream and cause frequent urination at night.

Lowering DHT can slow both processes. The medicine targets the conversion step, so it isn't a way of shutting down testosterone itself.

The main medicines

Two 5-ARIs are widely used in the U.S.:

• Finasteride: FDA-approved, in different strengths, for male pattern hair loss and for BPH. It's also used in some compounded topical hair-loss formulas.
• Dutasteride: FDA-approved for BPH as a daily capsule. Any use for hair loss in the U.S. is off-label.

What to expect

These medicines work slowly. Hair results usually take at least three months to appear and up to a year to judge, and benefits fade if you stop. For BPH, symptoms may take three to six months to improve, much slower than alpha-blocker medicines, which can help within days. 5-ARIs can shrink the prostate over time, which alpha-blockers don't do.

Side effects and cautions

Most men take a 5-ARI without problems, but known side effects include:

• Lower sex drive, erection difficulties and reduced ejaculate volume.
• Breast tenderness or enlargement.
• Depression or mood changes, which should be reported promptly.
• Allergic reactions, which are rare.

Important safety points

Women who are or may become pregnant should not handle crushed or broken finasteride tablets or leaking dutasteride capsules, because the drug can harm a male fetus. Men taking dutasteride shouldn't donate blood during treatment or for six months after stopping.

5-ARIs lower PSA, the blood test used in prostate cancer screening. Tell any clinician who orders a PSA, and the lab, that you take one, so the result can be interpreted correctly. The drug information for both medicines also notes a possible increased risk of high-grade prostate cancer, which is worth discussing before you start.

At HealifyMD, finasteride is one component of a compounded topical hair-loss treatment. Compounded products are not FDA-approved, and your clinician will review whether an oral, topical or non-hormonal option suits you best.

Because hair loss can also come from thyroid problems, iron deficiency, rapid weight loss or certain medicines, it's worth ruling those out before assuming the cause is hormonal. A clinician can help sort out which pattern you have.