Triptorelin acetate is a synthetic decapeptide analog of gonadotropin-releasing hormone (GnRH), classified as a GnRH agonist (GnRH-a). It’s structurally similar to the body’s natural GnRH but modified to resist enzymatic breakdown, giving it a much longer duration of action.
Mechanism of action
This is the interesting part pharmacologically — it works in two opposite phases:
Flare phase (first 1–2 weeks): Because it’s a GnRH agonist, initial exposure actually stimulates the pituitary gland, causing a transient surge in luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which temporarily increases testosterone or estrogen production.
Suppression phase (ongoing): With continuous exposure, GnRH receptors on the pituitary become desensitized and downregulated. This shuts down LH/FSH release, which in turn suppresses gonadal production of sex hormones — leading to castrate-level testosterone in men or menopause-level estrogen in women.
This is sometimes called “medical castration” or chemical suppression of the hypothalamic-pituitary-gonadal (HPG) axis.
Approved medical uses
Advanced prostate cancer — reduces testosterone, which fuels most prostate cancer growth
Central precocious puberty in children — pauses premature pubertal hormone activity
Endometriosis — suppresses estrogen to reduce lesion growth and pain
Uterine fibroids — shrinks fibroids before surgery in some protocols
Assisted reproduction (IVF) — controls hormone timing during ovarian stimulation protocols
Formulations
Typically given as an intramuscular or subcutaneous depot injection, in 1-month, 3-month, or 6-month long-acting release formulations (brand names include Decapeptyl, Diphereline, Trelstar, and Gonapeptyl, depending on the market).
Key clinical considerations
Often co-administered with an anti-androgen in prostate cancer patients during the first weeks to blunt the “flare” effect
Long-term suppression can cause hot flashes, bone density loss, and reduced libido, since it mimics a hypogonadal state
Requires medical supervision and monitoring of hormone levels
