GnRH agonist implant · early puberty
Built from nine amino acids, histrelin is a lab-made analog of gonadotropin-releasing hormone (GnRH) with greater potency than the natural hormone1. It is delivered from a small, flexible implant placed under the skin of the inner upper arm2. In the US it is used to pause central precocious puberty, when puberty starts too early because the brain's signal switches on too soon.
Puberty begins when the hypothalamus releases GnRH in pulses, prompting the pituitary to release LH and FSH, which in turn drive the ovaries or testes. Histrelin acts on the same pituitary receptors. At first it causes a short burst of LH, FSH, estrogen or testosterone, so signs of puberty can briefly worsen in the first week. Because the implant releases it continuously rather than in pulses, the receptors then down-regulate and the pituitary becomes desensitized; LH and FSH fall, and within about four weeks sex-hormone levels drop and pubertal changes stop progressing1. The effect is reversible: in long-term follow-up, the hormonal axis recovered normally after treatment ended3.
In a phase 3 study of 36 children with central precocious puberty, peak stimulated LH fell to suppressed levels within a month in children new to treatment and stayed suppressed in children already on treatment; estradiol and testosterone remained suppressed for the full year2. Children who continued with replacement implants for up to six years kept their hormones suppressed, the gap between bone age and actual age narrowed, and predicted adult height in a small group of girls rose by about 15 cm from baseline, with no harm to later recovery of the axis3.
In men with advanced prostate cancer, a histrelin implant designed for adults was also studied: all 134 evaluable men reached castrate testosterone levels by week four, and over 99% stayed there through 52 weeks4. These were open-label studies without control groups.
FDA-approved as Supprelin LA (2007) for children with central precocious puberty1. A related implant for advanced prostate cancer (Vantas, approved 2004) and an older injectable form (Supprelin, 1991) were also approved but have been discontinued.
The most common reaction is at the implant site, affecting about half of children, including bruising, pain, redness, swelling and problems with insertion or removal; implants can break during removal1. Label warnings include the initial hormone surge, mood and behavior changes such as irritability and aggression, seizures, severe skin reactions, and pseudotumor cerebri (raised pressure around the brain) with headache or vision changes. It is contraindicated in pregnancy.
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