How Gestrinone Affects SHBG
Gestrinone collapses SHBG, with binding capacity falling from 56.4 to 7.1 nmol/L within four weeks in one study. Total testosterone falls with it while free testosterone holds steady or rises, so total T is misleading on this drug.
The Mechanism
SHBG is made in the liver, and androgens suppress its production. Gestrinone is a potent androgen at the liver, and it also keeps estrogen low, which removes estrogen's normal push to raise SHBG.
Gestrinone does not appear to bind SHBG to a meaningful degree (Tamaya 1986, Dowsett 1986), so the drop is mainly a production effect. With less SHBG, a bigger fraction of your testosterone circulates free. That free fraction drives acne, hair growth and voice changes.
Expected Changes
Gestrinone 5 mg/week (Dowsett 1986, n=7):
- SHBG binding capacity 56.4 nmol/L at baseline
- 28.1 nmol/L after 1 week
- 7.1 nmol/L after 4 weeks, roughly an 87% fall
Oral 1.25 or 2.5 mg twice weekly (Dawood 1997, Venturini 1989):
- SHBG and total testosterone reduced
- Free testosterone not significantly changed, or slightly increased
Implants: no published data. Expect at least the oral effect.
Monitoring Guidance
- Test SHBG with total and free testosterone at baseline and at 6-8 weeks
- Use measured free testosterone, or calculate it from total T, SHBG and albumin
- Do not use total testosterone alone to judge androgen exposure on gestrinone
Management Strategies
- A very low SHBG with normal or high free testosterone confirms a strong androgen effect. Pair it with how your skin, hair and voice are doing
- If androgenic side effects are progressing, the SHBG result is supporting evidence for stopping or removal, not something to treat separately
- SHBG should recover after stopping. Recheck at 3 and 6 months
Full evidence review: Does gestrinone work for endometriosis?
Clinical Significance
SHBG suppression is the most reliable lab sign of gestrinone exposure and explains why total testosterone falls while androgenic side effects appear.
Frequently Asked Questions
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Quick Facts
Effect Direction
Severity
Dose-Dependent
Reversible