Histrelin Side Effects: What to Expect and When to Call Your Doctor

All medications have side effects, and Histrelin (Supprelin LA) is no exception. Because it works by suppressing the hormones that drive puberty — and because it is delivered via a surgically implanted device — its side effect profile is unique. Knowing what to expect can help you distinguish normal effects from warning signs that require a call to your doctor.

How Histrelin Causes Side Effects

Histrelin works by initially stimulating, then dramatically suppressing, the body's production of sex hormones — testosterone and estrogen. This "chemical castration" effect is therapeutic for CPP, but it also causes side effects similar to those experienced during menopause or androgen deprivation. Additionally, the implant delivery method introduces a unique set of insertion-site effects.

Common Side Effects of Histrelin (Supprelin LA)

The following side effects are common and generally expected during Histrelin therapy:

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Bruising, pain, soreness, tenderness, redness, swelling, or itching at the insertion site in the upper arm. These typically resolve within a few weeks.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop One of the most commonly reported side effects due to estrogen/testosterone suppression.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Irritability, emotional lability, crying, depression, and in rare cases aggression. GnRH agonists as a class are associated with psychiatric effects.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Reported in both adult and pediatric patients.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Light vaginal spotting or temporary breast tissue growth may occur during the first weeks as the drug initially stimulates hormones before suppressing them. This is expected and typically resolves within 4–6 weeks.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Commonly reported, related to hormonal changes.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Weight gain or loss reported in some patients.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Related to testosterone/estrogen suppression.

Serious Side Effects: When to Call Your Doctor Immediately

The following side effects are serious and require prompt medical attention:

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Reported in pediatric patients. Symptoms include severe headache, vision changes, blurred or double vision, ringing in the ears, and pain behind the eyes. Seek immediate evaluation if these occur.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop A rare but serious condition. Symptoms include sudden severe headache, visual disturbances, altered mental status, or collapse. Seek emergency care.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Reported in some patients. Seek immediate care. Patients with a history of seizures or epilepsy require closer monitoring.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop GnRH agonists can prolong the QT/QTc interval. Patients with existing cardiac conditions, electrolyte abnormalities, or those taking other QT-prolonging drugs need cardiac monitoring. Symptoms to report: chest pain, palpitations, fainting.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Occasionally the implant may migrate from its insertion site or come out through the skin. Contact your doctor if you notice changes in where the implant feels, or if you think it may have come out.

[@portabletext/react] Unknown block type "span", specify a component for it in the `components.types` prop Rare, typically mild and transient. ALT elevations above 3x normal occur in less than 1% of patients.

Long-Term Side Effects to Monitor

With long-term GnRH agonist therapy in children, bone mineral density can decrease due to reduced estrogen/testosterone levels. Your doctor will monitor bone density and may recommend calcium and vitamin D supplementation. Once Histrelin therapy is stopped and puberty resumes, bone density typically recovers over time.

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Side Effects After Implant Removal

After the implant is removed, puberty typically resumes within 3–12 months as GnRH suppression wears off. Some patients experience a temporary rebound in puberty signs. The effects of Histrelin are reversible once treatment is discontinued. For more about how Histrelin works, see our guide: What is Histrelin? Uses, dosage, and what you need to know.