Cimetidine blocks testosterone synthesis

Area of Science:

• Endocrinology
• Male Reproductive Health

Background:

• Cimetidine is a widely used medication with known endocrine side effects.
• Previous reports indicate varied endocrine dysfunctions, but typically normal gonadotropin and sex steroid levels.

Observation:

• A 66-year-old man experienced breast tenderness and sexual dysfunction after cimetidine use.
• This was associated with low plasma testosterone and elevated gonadotropin levels, suggesting a testicular issue.

Findings:

• Cimetidine discontinuation led to improved sexual function and normalized testosterone levels.
• Re-administration of cimetidine promptly caused recurrence of sexual dysfunction and low testosterone.
• A reversible defect in 17-beta-hydroxysteroid dehydrogenase was postulated as the mechanism.

Implications:

• Cimetidine can induce reversible hypogonadism and sexual dysfunction in men.
• The mechanism involves a reversible enzymatic defect affecting testosterone synthesis.
• Clinicians should consider cimetidine as a potential cause of sexual dysfunction in men.