5α-Reductase inhibitors

5α-Reductase inhibitors (5-ARIs), also known as dihydrotestosterone (DHT) blockers, are a class of medications that prevent the conversion of testosterone into dihydrotestosterone (DHT), a potent androgen involved in the development and progression of certain medical conditions. These inhibitors work by blocking the action of the enzyme 5α-reductase, which is responsible for the conversion process. There are two main types of 5α-reductase, type I and type II, with some inhibitors selectively blocking one type and others blocking both.

Medical Uses

5α-Reductase inhibitors are primarily used in the treatment of conditions that are exacerbated by DHT. The most common uses include:

• Benign prostatic hyperplasia (BPH) - Enlargement of the prostate gland can cause urinary problems. 5-ARIs can reduce prostate volume, improving urinary flow and symptoms.
• Prostate cancer - While not a first-line treatment, these medications can be used in combination with other therapies to manage prostate cancer.
• Pattern hair loss - Also known as androgenetic alopecia, 5-ARIs can slow hair loss and in some cases, promote hair regrowth.
• Hirsutism - Excessive hair growth in women in areas where hair is normally minimal or absent.

Mechanism of Action

5α-Reductase inhibitors function by binding to the active site of the 5α-reductase enzyme, preventing it from converting testosterone into DHT. Since DHT is a more potent androgen than testosterone, its reduction can alleviate symptoms associated with its excess. However, the effectiveness and side effects can vary depending on whether the inhibitor targets type I, type II, or both types of the enzyme.

Types

There are several 5α-reductase inhibitors available, including:

• Finasteride - Primarily a type II inhibitor, used for BPH, prostate cancer, and pattern hair loss.
• Dutasteride - Inhibits both type I and II enzymes, used for similar conditions as finasteride but may have a more comprehensive effect due to its dual inhibition.
• Epristeride - A type II inhibitor, used mainly in the treatment of BPH.

Side Effects

While 5α-Reductase inhibitors are generally well-tolerated, they can have side effects, including:

• Sexual dysfunction (e.g., decreased libido, erectile dysfunction)
• Gynecomastia (enlargement of breast tissue in men)
• Depression and mood changes
• Potential impact on prostate cancer risk, with ongoing debate and research into the effects of 5-ARIs on high-grade prostate cancer.

Controversies and Research

The use of 5α-Reductase inhibitors, particularly in the treatment of pattern hair loss, has been subject to controversy due to the potential for long-lasting side effects, sometimes referred to as post-finasteride syndrome. Research is ongoing to better understand the risks and mechanisms behind these adverse effects.

See Also

• Androgenetic alopecia
• Benign prostatic hyperplasia
• Prostate cancer
• Testosterone
• Dihydrotestosterone