How Do 5-Alpha Reductase Inhibitors Work?

Inhibitors of 5-alpha reductase are medications prescribed to treat prostate enlargement and male pattern hair loss (androgenic alopecia) in men. Inhibitors of 5-alpha reductase help shrink and slow down the growth of prostate tissue relieve associated urinary symptoms, and also reduce androgen-related hair loss.

The enzyme 5-alpha reductase catalyzes the conversion of the male hormone testosterone into dihydrotestosterone (DHT). Testosterone is responsible for growth in puberty and increased muscle mass, while dihydrotestosterone plays a role in fetal differentiation of external male genitals, male hair patterns, and prostate growth.

Inhibitors of 5-alpha reductase block the activity of 5-alpha reductase, reducing the concentration of dihydrotestosterone in the blood and in the prostate tissue. A decrease in DHT production controls the growth of prostate tissue and reduces hair loss.

Inhibitors of 5-alpha reductase are administered as oral tablets or capsules to treat the following conditions:

FDA-approved:

• Benign prostatic hyperplasia (prostate enlargement)
• Androgenic alopecia (hair loss) in men only

Off-label:

• Female hirsutism (abnormal male pattern hair growth in women)

Side effects of 5-alpha reductase inhibitors may include the following:

• Impotence
• Decrease in libido
• Ejaculation disorder
• Erectile dysfunction
• Breast disorders
• Breast enlargement
• Breast tenderness
• Male breast cancer
• Dizziness
• Cardiac failure
• Prostate cancer (high grade)
• Hypersensitivity reactions such as:
  • Rash
  • Urticaria (hives)
  • Pruritus (itching)
  • Localized edema
  • Angioedema (swelling in the tissue under the skin or mucous membranes)
  • Serious skin reactions
• Testicular pain and swelling
• Male infertility and/or poor seminal quality
• Hematospermia (blood in semen)
• Sexual dysfunction
• Orgasm disorders
• Depression

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of 5-alpha reductase inhibitor drugs include:

• Avodart
• dutasteride
• finasteride
• Propecia
• Proscar