Many men face the challenge of hair loss, but there are effective ways to protect your hairline, including medications known as 5-alpha reductase inhibitors (5ARIs). These medications have been demonstrated in placebo-controlled clinical trials to reduce hair loss and treat enlarged prostates.

Continue reading for a detailed guide on 5-alpha reductase inhibitors, including their mechanisms of action, common side effects, and possible harmful interactions.

FDA Approved for Over 25 Years

5-alpha reductase inhibitors are designed to treat male pattern hair loss, or androgenetic alopecia, and are also used to manage benign prostatic hyperplasia (BPH), a condition characterized by an enlarged prostate. Notable medications in this class include finasteride and dutasteride.

Finasteride was first approved by the Food and Drug Administration (FDA) in 1992. In addition to treating hair loss and BPH, 5-alpha reductase inhibitors are occasionally prescribed for conditions such as hyperandrogenism and hirsutism in women, as well as for hormonal treatment in transgender women.

How 5-Alpha Reductase Inhibitors Work

These inhibitors function by blocking 5-alpha reductase, an enzyme that converts testosterone into dihydrotestosterone (DHT). While DHT is essential for various bodily functions, including muscle growth and male characteristics, it is also linked to male pattern baldness and prostate growth.

In men with BPH, DHT accumulation in the prostate can lead to enlargement. By inhibiting the conversion of testosterone to DHT, 5-alpha reductase inhibitors can help reduce prostate size. Additionally, by preventing DHT from binding to androgen receptors in the scalp, these medications protect hair follicles in those genetically predisposed to hair loss.

The Difference Between Finasteride and Dutasteride

Currently, there are two FDA-approved 5-alpha-reductase inhibitors: finasteride and dutasteride. The primary distinction is that finasteride is typically prescribed for hair loss, while dutasteride is mainly used for managing enlarged prostate.

Interactions and Risks

5-alpha reductase inhibitors may pose certain risks and potential interactions. Notably, their use could increase the risk of prostate cancer. Men should monitor prostate-specific antigen (PSA) levels while on these medications, as changes may indicate the presence of prostate cancer.

Finasteride can also interact with St. John’s Wort, an herbal supplement used for various conditions, including depression.

Finasteride (Propecia and Proscar)

Finasteride is available under two brand names—Propecia for hair loss and Proscar for BPH—and is also sold as a generic. Developed in the 1970s, it was approved by the FDA in 1992 for BPH treatment and later for hair loss in 1997. The recommended dosage varies depending on the condition: 1 mg for hair loss and 5 mg for BPH.

Dutasteride (Avodart)

Dutasteride, patented in 1996 and approved by the FDA in 2001 as Avodart, is taken as a 0.5 mg oral capsule once daily. It alleviates symptoms of BPH, such as frequent or painful urination. Sometimes prescribed as a combination pill known as Jalyn®, which includes tamsulosin, dutasteride effectively treats BPH symptoms, though it is not FDA-approved for hair loss treatment.