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Growth hormone secretagogue — synthetic hexapeptide (research compound) · safety
Hexarelin side effects
The hexarelin side effects reported most often are prolactin rise, cortisol rise and growth-hormone response fading with use. The full list is below, with the cited trial report cited at the bottom of the page.
Rarer, but worth being able to spot: unknown long-term risk.
The sources describe these effects in relation to the dose and to the early weeks.
Hexarelin is a peptide six amino acids long, built in the early 1990s to trigger a growth-hormone pulse. Sellers pitch it as the hardest-hitting of the growth-hormone peptides, for muscle and recovery.
The pulse gets smaller as the doses repeat. On the only long course on record it had roughly halved by week 16, and came back only once the drug stopped. No trial turned that into a schedule, and none measured muscle.
At a glance
Common reactions listed
5
Serious reactions listed
1
Boxed warning
No label exists
Strongest source
limited human data
Common reactions
The full list, as reported across the available trial evidence. There is no approved label to read frequency bands off, so these are the trials’ own figures.
| Reaction | Frequency |
|---|---|
| Prolactin rise | Up to 180% above baseline at the 1.0 mcg/kg intravenous dose, with half that effect reached at 0.39 mcg/kg |
| Cortisol rise | A step increase of roughly 40% appearing at the 0.5 mcg/kg intravenous dose — the adrenal axis moving, not the pituitary one people are aiming at |
| Growth-hormone response fading with use | The response fell significantly by week 4 and roughly halved by week 16 of twice-daily dosing, returning to baseline four weeks after stopping |
| Blunted pituitary-adrenal response | A day of repeated injections blunted the growth-hormone response to a later intravenous dose and abolished the ACTH and cortisol response entirely |
| Altered sleep, with less slow-wave sleep | Named in the review literature; no incidence figure has been published for it |
Serious reactions to watch for
These are rarer, and they are the ones clinicians monitor for. Seek medical care if you have symptoms.
| Reaction | Frequency |
|---|---|
| Unknown long-term risk | No long-term safety data exists. The longest human course on record is 16 weeks, and it ended with the drug working less well than when it started — monitor |
When to seek medical care
The trial report does not give a separate list of serious reactions. There is also no approved label. That gap does not mean serious reactions cannot happen. This compound has been studied in fewer people and for less time than an approved drug.
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When these effects tend to occur
The cited evidence describes these effects in relation to the dose and to the early period of taking it, rather than as a constant background throughout.
When a study reports how side effects changed over time, it describes the group as a whole. It cannot predict one person’s experience.
Common questions
How long do hexarelin side effects last, and do they go away?
The sources do not commit to a set number of days. What they describe is a pattern — reactions cluster after you start and after each increase, then ease while the dose is held steady. Any page quoting an exact number of days is quoting something the sources do not say.
What are the most common hexarelin side effects?
Prolactin rise, cortisol rise, growth-hormone response fading with use and blunted pituitary-adrenal response — the table above has the rest, each with its frequency band and source.
Does hexarelin have a boxed warning?
No, because a boxed warning is part of an FDA-approved label and hexarelin has no approved label. That reflects what regulatory review has and has not covered, not a finding that serious risks were looked for and ruled out.
Can the hexarelin dose be lowered if side effects are hard to tolerate?
That decision belongs to the prescribing clinician. No approved schedule exists for this compound, so there is no labeled framework for adjusting a dose. That leaves the prescriber as the only place the decision can sit.
Does hexarelin cause hair loss?
Hair loss is not among the reactions listed on this page for hexarelin, because the cited trial report cited here does not carry it. Anything missing from the tables is outside what can be sourced here rather than ruled out, and a symptom that worries you belongs with a clinician.
Is fatigue a listed hexarelin side effect?
No — the cited trial report cited here does not list it. That describes what was reported, not proof that the symptom cannot happen.
Is constipation a listed hexarelin side effect?
Not separately. If a source groups stomach and gut events together, this page keeps that group intact. It does not invent named reactions the source never listed.
What should someone do about a serious hexarelin reaction?
Contact a clinician promptly, and emergency services if symptoms are severe or getting worse quickly. The section above describes what those reactions actually look like, so they can be spotted early rather than explained away.
Do the frequencies on this page mean the chance it happens to one person?
No. These figures describe groups in a study. A band shows how often a reaction appeared under that trial’s conditions. It cannot predict what will happen to one person.
Related
The schedule these reactions were recorded against, the comparisons, and the sourcing rules behind every grade on this page.
Hexarelin without an approved label: what exists instead
How the hexarelin trials escalated to their top arm
Hexarelin vial and water to an exact amount
Take the hexarelin arithmetic to any other vial
The full index behind the hexarelin page
The dated regulatory page for hexarelin and the rest
Why some hexarelin values are missing on purpose
- Massoud AF, Hindmarsh PC, Brook CG. Hexarelin-induced growth hormone, cortisol, and prolactin release: a dose-response study. J Clin Endocrinol Metab 1996;81(12):4338-41retrieved 2026-08-12Human trial
- Rahim A, O’Neill PA, Shalet SM. Growth hormone status during long-term hexarelin therapy. J Clin Endocrinol Metab 1998;83(5):1644-9retrieved 2026-08-12Human trial
- Maccario M, Veldhuis JD, Broglio F, Di Vito L, Arvat E, Deghenghi R, Ghigo E. Impact of two or three daily subcutaneous injections of hexarelin, a synthetic growth hormone (GH) secretagogue, on 24-h GH, prolactin, adrenocorticotropin and cortisol secretion in humans. Eur J Endocrinol 2002;146(3):310-8retrieved 2026-08-12Human trial
- Dominikowski A, Rękoś Z, Olejarz M, Szczepanek-Parulska E, Domin R, Ruchała M. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol 2026;17 — Table 1, hexarelin safety-signal rowretrieved 2026-08-12limited human data