Alarelin

What alarelin is

Alarelin, usually as alarelin acetate, is a synthetic nonapeptide, a derivative of gonadotropin-releasing hormone, GnRH. GnRH is the starting signal of the hormonal axis: it tells the pituitary gland to release LH and FSH, which control testosterone and sperm production in men and the menstrual cycle in women.

Clinically, alarelin is used like other GnRH agonists to temporarily shut this axis down: for endometriosis and hormone-dependent tumors, and in assisted reproduction to prevent premature ovulation. The papers on use in humans that we found come from China. It shares the receptor with gonadorelin, the replica of the body’s own GnRH, but not the goal.

How it works

Alarelin binds to the GnRH receptor of the pituitary gland. The same pattern applies to all GnRH agonists: after the first dose, LH, FSH and the sex hormones rise briefly. With continued dosing, the pituitary becomes desensitized, LH and FSH fall, and the production of testosterone and estrogen is suppressed. For the approved triptorelin, this is described in detail in the summary of product characteristics. For alarelin itself, the authors of a case report name exactly this effect: a reversible hypogonadism through desensitization of the pituitary.

This leads to the most important point for the assessment. Only GnRH given in short pulses has a stimulating effect, as with gonadorelin in pump therapy. Sustained stimulation of the receptor, by contrast, inhibits the axis. We found hardly any published data of its own on receptor binding and pharmacokinetics of alarelin in humans.

What the studies show

Duan 2010: alarelin versus triptorelin

The study compared the two agonists in the long protocol in 122 women aged 24 to 39 undergoing assisted reproduction; 78 women received alarelin, 44 triptorelin. In neither group was there a premature LH surge, premature ovulation or severe ovarian hyperstimulation syndrome. Oocyte count, embryo quality, implantation, pregnancy and miscarriage rates did not differ; cancelled cycles were more frequent under triptorelin. The groups were of unequal size, and the abstract does not describe random allocation.

Yuan 2025: a case of liver injury

A healthy 37-year-old participant in a phase I study in China developed acute hepatocellular injury after subcutaneous alarelin acetate. Causality was rated at 6 points on the RUCAM score, which counts as probable; the authors write “highly probable”. Liver values normalized within 18 days of discontinuation. The authors found genetic variants that could play a role and describe the case as the first documented of its kind. A single case does not demonstrate a risk at any particular frequency.

Where the data stop

• No study in men on testosterone or fertility. For the use around LH and testosterone suggested in the trade, we found not a single investigation.
• Hardly any data of its own. Receptor binding, pharmacokinetics and tolerability of alarelin in humans are barely published; phase I results are not available. We found no entry in ClinicalTrials.gov.
• Weak comparative study. The only comparative human study found has groups of unequal size and does not describe randomization.
• Products from the gray market. What is sold as a research peptide is not the medicine used in China; content and purity have not been independently tested.

Status, approval and legal

Alarelin is not approved in Germany, the EU or the US. It is not named either in Annex 1 of the German Prescription Medicines Ordinance or in the annex of the German Anti-Doping Act; the latter lists, among the releasing factors of LH, gonadorelin, leuprorelin and triptorelin, among others.

In sport, the situation is nonetheless clear: under S2.2.1, the WADA List 2026 prohibits GnRH and its agonistic analogues in men, explicitly not limited to the examples named. As a GnRH agonist, alarelin falls under this, in and out of competition.

Safety

There are no systematically published safety data on alarelin. The class effects of GnRH agonists are to be expected: with continuous dosing, sex hormones fall, with hot flashes, loss of libido and decreasing bone density; the summary of product characteristics of the related triptorelin additionally names an increased risk of depression.

For alarelin itself, there is a case of severe liver injury in a healthy trial participant that regressed after discontinuation. Anyone using it in men to stimulate LH or testosterone risks, according to the class principle, the opposite: suppression of their own hormone production. Hormone protocols belong under medical supervision.

Sources

• Duan JL et al., Zhonghua Nan Ke Xue 2010 – alarelin versus triptorelin in the long protocol of assisted reproduction, 122 patients
• Yuan F et al., Front Med 2025 – liver injury under alarelin acetate, case report and literature review
• Summary of product characteristics Pamorelin LA 3.75 mg (triptorelin, as of 04/2026) – mechanism of action of GnRH agonists
• WADA – Prohibited List 2026, S2.2.1 Testosterone-stimulating peptides in males
• German Anti-Doping Act, annex – releasing factors of CG and LH (list by name)
• German Prescription Medicines Ordinance (AMVV), Annex 1