Nafarelin (Synarel)

Safety Summary

The adverse effect profile of nafarelin is characteristic of the GnRH agonist class and is primarily driven by the intended pharmacological effect of sex steroid suppression (hypoestrogenism in females, hypogonadism in males). The most common effects -- hot flashes, vaginal dryness, mood changes, decreased libido, and headache -- are predictable consequences of estrogen/testosterone suppression and are generally manageable with symptomatic treatment or by limiting treatment duration (FDA label; PMID 2140979, Goa & Heel 1990 review). Bone mineral density (BMD) loss is the most clinically significant chronic risk, with 3-11% trabecular BMD loss over 6 months documented in endometriosis RCTs; this is partially reversible after discontinuation but may not fully recover, particularly with repeated courses (PMID 9252932, nafarelin vs leuprolide BMD study; NDA Medical Review). BMD loss can be mitigated with add-back therapy (norethisterone; PMID from Abdalla et al., Clin Endocrinol 1992, https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2265.1992.tb02338.x). Serious but rare postmarketing events include pituitary apoplexy, thromboembolic events, seizures, severe psychiatric reactions (including suicidal ideation), and idiopathic intracranial hypertension (FAERS signal 2021). No tolerance/tachyphylaxis has been observed with continuous use up to 12 months (NDA Medical Review). Upon discontinuation, gonadotropin and sex steroid recovery typically occurs within weeks to months, with return of menses or pubertal progression (FDA label). No carcinogenicity signal has been identified in rodent studies or post-marketing surveillance through early 2026 (FDA label; EMA PRAC minutes Jan 2025; PMC12250665, pharmacovigilance comparison study). Safety data derive from RCTs in approximately 1509 adult endometriosis patients and 155 pediatric CPP patients, plus decades of post-marketing surveillance (FDA label).