Buserelin
Also known as: Buserelin Acetate · Suprefact (brand) · Suprecur (brand) · Profact (brand)
Buserelin is a synthetic GnRH agonist analog, carrying a D-serine(tert-butyl) substitution at position 6 and a des-glycine-10 ethylamide C-terminal modification — structurally related to Leuprolide Acetate (D-Leu6) and Alarelin (D-Ala6), also built on this site. At Verified Peptides, we want to be direct about a genuine regulatory distinction: unlike Leuprolide, Triptorelin, Cetrorelix, and Ganirelix (all FDA-approved and built elsewhere in this catalog), Buserelin has never been approved for human use in the United States or Australia, despite being widely approved and used in the UK, Ireland, other European countries, Canada, and many other regions since 1984 under brand names including Suprefact and Suprecur. Notably, Buserelin was the reference GnRH agonist compared directly against Ganirelix in Ganirelix's own pivotal FDA approval trial. Research-grade material sold here is a separate product intended solely for laboratory research.
What is Buserelin?
Buserelin is a synthetic nonapeptide-ethylamide GnRH agonist analog, carrying a D-serine substitution (with a tert-butyl ether protecting the serine side-chain hydroxyl) at position 6, replacing native GnRH's glycine, along with a des-glycine-10 ethylamide C-terminal modification in which the native terminal glycinamide is replaced by direct ethylamide attachment to proline-9. This is the same general modification strategy used by Leuprolide Acetate (D-leucine-6) and Alarelin (D-alanine-6), both also built on this site — three chemically distinct single-position substitutions converging on the same general pharmacological outcome.
At Verified Peptides, we want to directly flag a genuine and important regulatory distinction for this specific compound: Buserelin was first described in 1976 and introduced into medical use in 1984, making it one of the earliest GnRH agonists to reach clinical practice, predating even Leuprolide's 1985 US approval. However, Buserelin has never been approved for human use in the United States or Australia, despite being widely marketed and used in the United Kingdom, Ireland, other European countries, Canada, New Zealand, South Africa, Latin America, and parts of Asia under brand names including Suprefact, Suprecur, and Profact. This is a genuinely different regulatory pattern from Alarelin (approved only in China) — Buserelin is approved essentially everywhere except the US and Australia specifically.
Chemically, Buserelin has molecular formula C60H86N16O13, molecular weight approximately 1239.45 g/mol (independently cross-calculated, matching literature figures exactly), CAS number 57982-77-1, PubChem CID 50225.
We independently verified this molecular weight atom-by-atom from the formula: 60 carbon (12.011 each), 86 hydrogen (1.008 each), 16 nitrogen (14.007 each), and 13 oxygen (15.999 each) sum to approximately 1239.45 g/mol, matching the literature figure exactly, giving us confidence in this compound's chemical identifiers without needing to flag any vendor discrepancy, unlike the mismatch we identified and corrected for Alarelin elsewhere in this phase.
Key Benefits & Mechanisms
Mechanism of action
Buserelin acts as an agonist at the GnRH receptor, the same receptor targeted by native Gonadorelin and by the other GnRH agonist analogs profiled on this site. As covered in more depth in this catalog's Gonadorelin, Triptorelin, Alarelin, and Leuprolide Acetate profiles, sustained (non-pulsatile) GnRH receptor stimulation produces an initial transient surge in LH, FSH, and downstream sex hormone production, followed by pituitary receptor downregulation and desensitization, ultimately suppressing gonadotropin secretion and gonadal sex hormone production to castrate or near-castrate levels.
A notable pharmacological detail specific to Buserelin's clinical development is that it has been studied and used via both subcutaneous injection and intranasal spray administration routes — an unusual delivery route for a peptide drug, since peptides are generally poorly absorbed across mucosal membranes. Buserelin's original clinical studies found that subcutaneous administration achieved and maintained lower, more consistently suppressed testosterone levels than intranasal delivery, and injectable/depot formulations have become the predominant clinical delivery route in practice, though the intranasal formulation (Suprecur, used for some indications including endometriosis and IVF protocols) remains a genuinely distinctive feature of Buserelin's clinical history among the GnRH agonists in this catalog.
Buserelin's use as the long-agonist-protocol reference comparator in Ganirelix's pivotal antagonist trial is mechanistically notable: that trial combined Buserelin with recombinant FSH in a traditional 'long protocol,' starting agonist administration in the cycle preceding ovarian stimulation to achieve pituitary downregulation before stimulation begins, in contrast to the antagonist approach of starting treatment only once stimulation is already underway. This difference in treatment timing and overall cycle duration, not merely a difference in receptor mechanism, is part of what the efficacy-versus-safety tradeoff observed in that trial reflects.
Research Summary
At Verified Peptides, we think Buserelin has a substantial though methodologically somewhat older evidence base compared to some of the other GnRH agonists in this catalog. The key early efficacy citation is Soloway (1988, American Journal of Clinical Oncology, PMID 3133944, volume 11, supplement 1, pages S29-32), evaluating 207 patients with advanced prostate cancer receiving buserelin via subcutaneous or intranasal routes, compared against historical control groups from the National Prostate Cancer Project (patients previously treated with diethylstilbestrol or surgical orchiectomy) rather than a concurrent randomized comparator arm. The study found castrate testosterone levels (below 100 ng/dl) achieved in 90% of patients by week 4, with subcutaneous administration maintaining lower testosterone levels than intranasal delivery, minimal toxicity (hot flushes in 72%, injection site reactions in 12%), and treatment efficacy judged equivalent to the historical diethylstilbestrol/orchiectomy control groups with no significant difference in progression-free survival.
We want to be direct that this historical-control study design, common in prostate cancer research during this earlier era before placebo-controlled or head-to-head randomized trials became the universal standard, is methodologically less rigorous than the concurrent randomized controlled trials we have cited for some other GnRH agonists and antagonists in this catalog (including Cetrorelix's and Ganirelix's pivotal trials) — a genuine limitation worth noting rather than obscuring. That said, we also want to highlight a specific, more rigorous connection: Buserelin was the reference long-agonist-protocol comparator directly used in Ganirelix's own pivotal randomized FDA/EMA approval trial (European Orgalutran Study Group, 2000, PMID 10875855, also cited on this site's Ganirelix profile), giving Buserelin an unusually direct link to a genuinely rigorous, concurrent randomized comparison, even though that specific trial's primary purpose was establishing Ganirelix's efficacy and safety rather than Buserelin's. We also want to note that Buserelin's broader independently published literature extends across its several approved indications beyond prostate cancer, including clinical research in endometriosis symptom management, premenopausal breast cancer (where ovarian estrogen suppression can serve a therapeutic role analogous to testosterone suppression in prostate cancer), and its use within various assisted reproduction stimulation protocols, reflecting several decades of accumulated clinical experience across the regions where it has been approved and used, even without a US regulatory record specifically.
No FDA approval exists for Buserelin in the United States. At Verified Peptides, we sell research-grade Buserelin exclusively for laboratory research.
Common Stacks
Lesser-Known Facts About Buserelin
Buserelin's intranasal spray formulation (marketed as Suprecur for some indications) is a genuinely distinctive feature among GnRH agonists — peptides are generally poorly absorbed across the nasal mucosa due to their size and susceptibility to enzymatic degradation, and achieving clinically meaningful systemic absorption via this route required specific formulation approaches, illustrating an early example of non-injectable peptide drug delivery research that predates much of the more recent interest in alternative peptide administration routes.
Buserelin's absence from the US market is not attributable to any documented safety or efficacy concern specific to the compound; rather, it reflects the practical reality that once other GnRH agonists (Leuprolide, and later Goserelin, Triptorelin, and Histrelin) had already secured FDA approval and established market presence in the United States, there was limited commercial incentive for Buserelin's manufacturer to pursue a separate, costly FDA approval process for a therapeutically similar product in an already well-served market.
Buserelin is also studied in veterinary contexts (particularly in reproductive management of livestock and companion animals) and continues to be an active subject of formulation research, including sustained-release implant and injectable microsphere development, mirroring the same formulation-innovation trajectory seen with Leuprolide and Triptorelin elsewhere in this catalog.
Purity & Sourcing Considerations
At Verified Peptides, we require independent third-party HPLC purity testing and mass spectrometry identity confirmation for every batch of research-grade Buserelin we offer, with a Certificate of Analysis (COA) available for each lot. As a peptide with a D-amino acid substitution carrying a tert-butyl ether side-chain modification, pyroglutamate N-terminus, and C-terminal ethylamide, all of these features should be confirmed as part of identity testing, since the specific D-serine(tert-butyl)-6 substitution is what distinguishes Buserelin from closely related GnRH agonist analogs with different position-6 substitutions.
We source exclusively from manufacturers operating under Good Manufacturing Practice (GMP)-aligned quality systems, and every lot is independently verified rather than accepted solely on a supplier's internal documentation. Researchers should always request and review the specific COA for the lot they receive, confirming purity percentage and molecular identity before use in any experimental protocol, and specifically noting whether the material is formulated for injectable or intranasal research applications, given Buserelin's history of use via both routes.
Storage & Stability
Lyophilized Buserelin is stable when stored at -20°C, protected from light and moisture. At Verified Peptides, we ship lyophilized peptide with appropriate cold-chain packaging to preserve stability in transit.
Once reconstituted, solution should be stored refrigerated at 2–8°C and used within the timeframe indicated on the product's documentation, avoiding repeated freeze-thaw cycles, consistent with standard handling practices for the other GnRH agonist peptides in this catalog.
Frequently asked questions about Buserelin
What is Buserelin and how does it differ from Leuprolide or Alarelin?
Buserelin is a synthetic GnRH agonist analog carrying a D-serine(tert-butyl) substitution at position 6, distinguishing it from Leuprolide (D-leucine-6) and Alarelin (D-alanine-6). All three use a similar des-glycine-10 ethylamide modification and achieve the same general therapeutic goal through different specific chemistry.
Is Buserelin FDA approved?
No. Despite being one of the earliest GnRH agonists introduced into clinical use (1984) and widely approved in the UK, Ireland, other European countries, Canada, and many other regions, Buserelin has never been approved for human use in the United States or Australia.
What evidence supports Buserelin's efficacy?
Soloway (1988, PMID 3133944) found castrate testosterone levels achieved in 90% of 207 patients by week 4, compared to historical controls treated with diethylstilbestrol or orchiectomy. This was a historical-control comparison rather than a concurrent randomized trial, a genuine methodological limitation worth noting.
How is Buserelin connected to Ganirelix's approval history?
Buserelin was the long-agonist-protocol reference comparator directly used in Ganirelix's own pivotal randomized FDA/EMA approval trial (European Orgalutran Study Group, 2000), giving Buserelin an unusually direct link to a rigorous, concurrent randomized clinical comparison.
What administration routes have been used for Buserelin?
Both subcutaneous injection and intranasal spray, an unusual delivery route for a peptide. Subcutaneous administration was found to maintain lower, more consistent testosterone suppression than intranasal delivery in early clinical studies.
Why was Buserelin never brought to the US market?
This does not appear to reflect any documented safety or efficacy concern. Once other GnRH agonists (Leuprolide, Goserelin, Triptorelin, Histrelin) had already secured FDA approval, there was limited commercial incentive to pursue a separate US approval for a therapeutically similar product.
What conditions is Buserelin approved to treat in the regions where it is available?
Approved indications include hormone-responsive cancers (prostate and premenopausal breast cancer), endometriosis, uterine fibroids, and female infertility via assisted reproduction, with off-label use in precocious puberty and gender-affirming hormone therapy contexts.
What treatment timing distinguished the long-agonist protocol using Buserelin from antagonist protocols like Ganirelix?
The long-agonist protocol starts Buserelin in the cycle preceding ovarian stimulation to achieve pituitary downregulation before stimulation begins, while antagonist protocols start treatment only once stimulation is already underway — a difference in overall treatment duration and timing, not just receptor mechanism.
Legal & research status: Buserelin is approved for human medical use in the United Kingdom, Ireland, other European countries, Canada, New Zealand, South Africa, and many other regions (brand names including Suprefact, Suprecur, and Profact), but has never been FDA-approved for human use in the United States, and is also not approved in Australia. Material sold as a research compound is offered strictly for laboratory and research use, not for human consumption or therapeutic use.