Definition: A GnRH agonist is a drug that acts like gonadotropin-releasing hormone, the brain signal that drives LH and FSH release. Given continuously, it first raises sex hormones and then lowers them. Examples are leuprolide (Lupron Depot) and goserelin (Zoladex), given as long-acting depot shots or implants.
| Product | Approved uses (short form) |
|---|---|
| Lupron Depot 3.75 mg (leuprolide) | Endometriosis; with iron, raising blood counts before surgery for fibroids |
| Zoladex 3.6 mg (goserelin) | Prostate cancer, endometriosis, thinning the uterine lining before ablation, advanced breast cancer |
The Lupron Depot label (section 5.5) says sex hormones briefly rise above baseline after the first dose, so symptoms may get worse in the first days before they ease. The lasting effect is a low-estrogen state, which the label says reduces bone density, and some loss may not reverse. Treatment length is limited for this reason.
For endometriosis, norethindrone add-back reduces the loss, and retreatment is only with add-back after a bone density check. Other Lupron Depot warnings include harm to an unborn baby, severe skin reactions, seizures and depression. The label says it is not a contraceptive and advises a non-hormonal method if contraception is needed.
A GnRH antagonist blocks the same receptor right away, without the first rise. That is why antagonists are used in IVF to stop early ovulation within a cycle. For the general idea, see receptor agonist. Depot shots and implants are given weeks or months apart, so logging the date of each one keeps the next due date clear.
Read more on Dose Track: Lupron Depot side effects · Zoladex side effects · Lupron Depot vs Zoladex