Leuprolide is a synthetic nonapeptide that mimics gonadotropin-releasing hormone (GnRH, also called LHRH). Outside the United States it is usually written leuprorelin. Takeda patented it in 1973, and the FDA approved the first formulation (Lupron, for advanced prostate cancer) on April 9, 1985, per StatPearls. It was the first GnRH agonist to reach clinical development, and it is sold today under brand names including Lupron, Eligard, Fensolvi, and Camcevi.
This is an approved prescription drug, not a research chemical. It is also one of the better-studied peptides in this class.
What it is
The molecule is a nine-amino-acid analog of natural GnRH, with the sequence Pyr-His-Trp-Ser-Tyr-D-Leu-Leu-Arg-Pro-NHEt. Swapping in a D-leucine residue and modifying the C-terminus makes it far more potent and longer-lasting than the natural hormone, which the body releases in short pulses and clears quickly. It is given by intramuscular or subcutaneous injection, and depot formulations release the drug over 1, 3, 4, or 6 months (StatPearls, DrugBank DB00007).
How it works
The mechanism is a two-phase effect that trips up intuition. Natural GnRH is released in pulses, and that pulsing is what keeps the pituitary producing luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Leuprolide floods the receptor continuously instead. At first this stimulates the pituitary, so LH, FSH, and the sex steroids downstream (testosterone in men, estrogen in women) spike. That early rise is the flare. With continued dosing the pituitary GnRH receptors desensitize and downregulate, and gonadotropin and gonadal steroid levels fall to castrate range. The Takeda/Abbott depot literature describes the flare appearing in roughly the first week and suppression reaching chemical-castration levels by about the fourth week (F&S Reports / ScienceDirect).
Approved uses and evidence
Leuprolide is FDA-approved for:
- Advanced prostate cancer (lowering testosterone slows hormone-sensitive disease)
- Endometriosis
- Uterine fibroids (leiomyomata)
- Central precocious puberty in children
The StatPearls review also lists documented off-label uses, including breast cancer, ovarian suppression, gender-affirming hormone therapy, and treatment of certain paraphilias. The evidence base spans decades of trials and routine clinical use across these indications (StatPearls).
Because it is a prescription medicine with a long safety record, its side-effect profile is also well characterized in the literature. We do not give medical or dosing advice here; any clinical use is a matter for a licensed prescriber.
WADA and anti-doping status
Leuprolide is prohibited in sport. WADA added GnRH analogs to its Prohibited List effective January 1, 2016, and lists them among testosterone-stimulating substances. The concern is the flare: a short course can transiently push the body's own LH and testosterone up, which is why GnRH agonists are treated as indirect androgen-doping or masking agents. WADA notes that all metabolites of these analogs are also prohibited and that detecting them constitutes a doping offense (WADA research summary).
The quality and testing angle
For an approved injectable, identity and purity are handled through pharmaceutical manufacturing and regulatory oversight. That is not the case for material sold through the gray peptide market under the "leuprorelin" or CAS 53714-56-0 label. Anything sold that way is research-use-only and not intended for human consumption, and it carries no guarantee that the vial contains the stated peptide at the stated purity. The questions that matter for any such product are the same ones we track across vendors: a current certificate of analysis (COA), independent third-party identity and purity testing, and the consistency of those results over time. peptideone aggregates that kind of testing and vendor-rating data so it can be compared in one place; we run no tests of our own.
Nothing here is medical, dosing, or efficacy advice.