The peptide and hormone library
30 peptides and 8 hormones relevant to men's health and performance: what each one is, what the evidence shows, and what to watch for.
Peptides
Short chains of amino acids that act as signals in the body.
Growth hormone secretagogues
Compounds that prompt the pituitary to release more of the body's own growth hormone.
SermorelinGRF 1-29A short copy of the hormone that tells the pituitary to release growth hormone.
- What it is
- Sermorelin is the first 29 amino acids of growth-hormone-releasing hormone (GHRH), the part that carries its activity. It binds GHRH receptors in the pituitary and triggers growth hormone release in the body's natural pulses, so the body's own feedback limits stay in place.
- What the evidence shows
- Good evidence that it raises growth hormone and IGF-1 in people. Evidence for body composition, sleep or recovery benefits in healthy adult men is small and mostly from older studies.
- What to watch for
- Injection-site reactions, flushing and headache are the common complaints. Raised IGF-1 should be monitored with blood work.
TesamorelinEgriftaA stabilised GHRH analogue used to cut visceral belly fat.
- What it is
- Tesamorelin is a full-length GHRH molecule modified to last longer in the blood. Like sermorelin, it works through the pituitary, so growth hormone still rises and falls in pulses.
- What the evidence shows
- Large randomised trials showed meaningful reductions in visceral (deep abdominal) fat in people with HIV-associated fat gain. Evidence for general fat loss or performance in healthy men is more limited.
- What to watch for
- Joint pain, fluid retention, numbness or tingling, and raised blood sugar. Not suitable for people with active cancer, as growth signals may feed tumour growth.
CJC-1295Modified GRF 1-29 (no DAC); CJC-1295 with DACA long-acting GHRH analogue, usually discussed alongside ipamorelin.
- What it is
- CJC-1295 is a modified GHRH fragment. The version with DAC binds to albumin in the blood and can last for days; the version without DAC (often called mod GRF 1-29) lasts minutes, closer to natural signalling.
- What the evidence shows
- Early human studies confirmed sustained rises in growth hormone and IGF-1. There are no completed trials showing benefits for muscle, fat loss or recovery.
- What to watch for
- Flushing, fluid retention and injection-site reactions. Long-acting versions blunt natural growth hormone pulses. Purity varies widely between sources.
IpamorelinA selective growth hormone secretagogue that acts on the ghrelin receptor.
- What it is
- Ipamorelin mimics ghrelin at the receptor that triggers growth hormone release. It is described as selective because, unlike older peptides in its class, it raises cortisol and prolactin very little.
- What the evidence shows
- Animal and early human data show reliable growth hormone release. Human evidence for muscle, fat or recovery outcomes is lacking.
- What to watch for
- Increased hunger, water retention and headache. Purity varies widely between sources.
IbutamorenMK-677An oral ghrelin mimic that keeps growth hormone and IGF-1 elevated.
- What it is
- Ibutamoren is a small molecule taken by mouth, not a peptide, that activates the ghrelin receptor for around a day per dose. It is included here because it is so often used alongside peptides.
- What the evidence shows
- Human trials show lasting increases in growth hormone and IGF-1 and some gains in lean mass, without clear improvements in strength or function.
- What to watch for
- Strong appetite increase, fluid retention, and reduced insulin sensitivity with higher blood sugar. A trial in older adults raised concerns about heart failure.
Recovery and repair
Peptides studied for tissue healing, inflammation and skin repair.
BPC-157Body Protection Compound 157A gut-derived peptide fragment studied for tendon, ligament and gut healing.
- What it is
- BPC-157 is a 15-amino-acid sequence derived from a protein found in gastric juice. In animal studies it appears to support blood-vessel growth and tissue repair.
- What the evidence shows
- Almost all evidence is from rodent studies. Human data is limited to very small pilot reports, with no controlled trials showing benefit.
- What to watch for
- Long-term human safety is unknown. Because it promotes blood-vessel growth, there is a theoretical concern for anyone with cancer. Purity and labelling vary widely between sources.
TB-500Thymosin beta-4 fragmentA fragment of thymosin beta-4, a protein involved in cell movement and wound repair.
- What it is
- Thymosin beta-4 helps cells move into damaged tissue and organise repair. TB-500 is a synthetic fragment of the region thought to drive this effect.
- What the evidence shows
- Animal studies suggest faster wound and muscle repair. Clinical trials of the full-length protein for eye injuries and heart damage showed mixed results. TB-500 itself has no human trials.
- What to watch for
- Unknown long-term safety in humans and the same theoretical cancer concern as other repair-promoting peptides.
GHK-CuCopper peptideA copper-binding peptide found naturally in blood, best known in skincare.
- What it is
- GHK is a three-amino-acid peptide that binds copper. Levels fall with age. In lab studies it influences collagen production and wound-healing genes.
- What the evidence shows
- Topical use has reasonable small-study support for skin firmness and fine lines. Evidence for injected use, including for hair or recovery, is preclinical.
- What to watch for
- Topical forms are generally well tolerated. Injection can cause local pain, and contamination is a risk with poorly made injectable products.
KPVLys-Pro-ValA tiny anti-inflammatory fragment of a skin-pigment hormone.
- What it is
- KPV is the last three amino acids of alpha-MSH. It appears to calm inflammatory signalling inside cells without affecting skin pigment.
- What the evidence shows
- Promising results in animal models of gut inflammation and skin irritation. No human trials have been completed.
- What to watch for
- Human safety is essentially unstudied.
Metabolic and body composition
Appetite, blood sugar and fat-loss signalling.
SemaglutideOzempic, Wegovy, RybelsusA once-weekly GLP-1 medicine for weight loss and blood sugar control.
- What it is
- Semaglutide mimics GLP-1, a gut hormone that slows stomach emptying, increases fullness and helps the pancreas release insulin when blood sugar is high.
- What the evidence shows
- Large trials show average weight loss around 15% over about 16 months alongside lifestyle changes, plus reduced heart attack and stroke risk in high-risk patients.
- What to watch for
- Nausea, constipation and diarrhoea are common early on. Rapid weight loss can include muscle, so resistance training and protein matter. Rare risks include pancreatitis and gallbladder problems.
TirzepatideMounjaro, ZepboundA weekly dual-hormone medicine that acts on both GLP-1 and GIP receptors.
- What it is
- Tirzepatide activates the GLP-1 receptor and a second gut-hormone receptor, GIP. The combination appears to produce stronger appetite and blood sugar effects than GLP-1 alone.
- What the evidence shows
- Trials show average weight loss of around 20% at the highest dose. In a head-to-head trial it produced more weight loss than semaglutide.
- What to watch for
- Side effects are similar to semaglutide and mostly digestive. The same advice on preserving muscle applies.
RetatrutideLY3437943An experimental triple-hormone weight-loss injection.
- What it is
- Retatrutide acts on GLP-1, GIP and glucagon receptors. Adding glucagon is thought to raise energy use and help clear liver fat, on top of reducing appetite.
- What the evidence shows
- Phase 2 and phase 3 results show some of the largest average weight losses seen with any medicine so far.
- What to watch for
- Still investigational, so long-term safety data are limited. Side effects in trials were mostly digestive, with some increases in heart rate.
CagrilintideOften paired with semaglutide as CagriSemaA long-acting copy of amylin, a fullness hormone released with insulin.
- What it is
- Amylin slows stomach emptying and signals fullness to the brain through a different route from GLP-1. Cagrilintide is a weekly amylin analogue designed to be paired with semaglutide.
- What the evidence shows
- Phase 3 trials of the combination showed average weight loss of over 20%. In a head-to-head trial it fell slightly short of tirzepatide.
- What to watch for
- Digestive side effects were common in trials, more so than with either drug alone. Long-term data are still building.
LiraglutideVictoza, SaxendaThe earlier, once-daily GLP-1 medicine.
- What it is
- Liraglutide works the same way as semaglutide but is cleared faster, so it is injected daily rather than weekly.
- What the evidence shows
- Average weight loss in trials was around 8%, less than newer options, but it has the longest safety record in its class.
- What to watch for
- Mostly digestive side effects. Daily injections can be harder to stick with than weekly ones.
AOD-9604Growth hormone fragment 177-191A fragment of growth hormone once developed as a fat-loss drug.
- What it is
- AOD-9604 is a modified piece of the end of the growth hormone molecule. The idea was to keep growth hormone's fat-burning effect without its effects on growth or blood sugar.
- What the evidence shows
- Animal studies were promising, but larger human trials did not show meaningful weight loss compared with placebo.
- What to watch for
- It appeared well tolerated in trials. The main issue is that it did not work in people.
Mitochondrial
Peptides that act on mitochondria, the parts of the cell that produce energy.
SS-31ElamipretideA peptide that targets the inner membrane of mitochondria.
- What it is
- Elamipretide binds cardiolipin in the inner mitochondrial membrane, helping stabilise the machinery that produces cellular energy.
- What the evidence shows
- Shown to improve muscle strength in Barth syndrome, a rare inherited mitochondrial disease. Trials in heart failure and age-related muscle decline have had mixed results, and evidence in healthy people is lacking.
- What to watch for
- Injection-site reactions are common. Benefits outside rare mitochondrial disease are unproven.
MOTS-cA small peptide made by mitochondria that may act like an exercise signal.
- What it is
- MOTS-c is coded by mitochondrial DNA rather than the cell nucleus. In animals it appears to improve how muscle handles glucose, and levels rise during exercise.
- What the evidence shows
- Mouse studies show better insulin sensitivity and exercise capacity. Human evidence is limited to measuring natural levels, not giving it as a treatment.
- What to watch for
- Human safety from injection is unknown.
Cognitive
Focus, memory, stress and brain plasticity.
SemaxA nasal peptide used in Russia for stroke recovery and focus.
- What it is
- Semax is a modified fragment of ACTH, a stress-axis hormone, altered to remove hormonal activity. It appears to raise BDNF, a protein that supports brain plasticity.
- What the evidence shows
- Most clinical research comes from Russian studies in stroke recovery and cognitive impairment. Independent trials in healthy people are lacking.
- What to watch for
- Generally reported as well tolerated, but the evidence base outside Russia is thin.
SelankA nasal peptide developed in Russia for anxiety without sedation.
- What it is
- Selank is a modified version of tuftsin, a natural immune peptide. It appears to influence GABA signalling and serotonin balance.
- What the evidence shows
- Small Russian studies suggest anxiety reduction comparable to some medicines without drowsiness. Evidence outside Russia is minimal.
- What to watch for
- Reported side effects are mild, but long-term data are lacking.
DihexaPNB-0408An experimental compound studied for memory and new connections between brain cells.
- What it is
- Dihexa is a modified fragment of angiotensin IV, developed by researchers studying memory. It appears to strengthen signalling through hepatocyte growth factor (HGF), which helps neurons form new connections.
- What the evidence shows
- Rodent studies show improved learning and memory, including in models of dementia. There are no published human trials.
- What to watch for
- Human safety is unstudied. Because the HGF pathway it amplifies is also involved in some cancers, there is a theoretical risk of promoting tumour growth.
Testosterone and fertility signalling
Signals that drive the body's own testosterone and sperm production.
hCGHuman chorionic gonadotropin; Pregnyl, OvidrelA hormone that mimics LH, the signal telling the testes to make testosterone.
- What it is
- hCG acts on the same receptor as luteinising hormone (LH). In men it stimulates the testes to make testosterone and supports sperm production. It is often used alongside testosterone therapy to keep the testes active and preserve fertility.
- What the evidence shows
- Well established for restoring testosterone and fertility in men with pituitary-related deficiency. Commonly used with testosterone therapy, though larger trials in that setting are limited.
- What to watch for
- Can raise oestrogen, causing breast tenderness or fluid retention. Requires blood monitoring under a prescribing doctor.
GonadorelinSynthetic GnRHA copy of the brain's master signal for testosterone production.
- What it is
- Gonadorelin is identical to GnRH, the hormone the hypothalamus releases in short pulses to trigger LH and FSH from the pituitary. Short pulses stimulate the system; continuous exposure shuts it down.
- What the evidence shows
- Proven to stimulate LH and FSH when given in pulses. Evidence for maintaining testicular function during testosterone therapy is limited compared with hCG.
- What to watch for
- Very short-acting, so timing matters. Headache and injection-site reactions are the most common effects.
Kisspeptin-10A brain signal that sits upstream of the entire testosterone axis.
- What it is
- Kisspeptin activates the neurons that release GnRH. Kisspeptin-10 is the shortest active fragment of the natural hormone.
- What the evidence shows
- Human research studies show it reliably raises LH and testosterone in men in the short term. Longer-term outcomes have not been studied.
- What to watch for
- Effects fade with repeated dosing in some studies. Not available as a licensed product.
Sexual health
Peptides acting on desire, arousal and bonding.
BremelanotidePT-141, VyleesiA melanocortin peptide that acts on desire in the brain rather than blood flow.
- What it is
- Bremelanotide activates melanocortin receptors in the brain involved in sexual motivation. Unlike PDE5 drugs such as sildenafil, it does not act on blood vessels in the penis.
- What the evidence shows
- Effective in trials in women with low sexual desire. Earlier studies in men with erectile dysfunction showed some effect, but it was not developed further for men.
- What to watch for
- Nausea is very common, along with flushing and a short-lived rise in blood pressure. Not suitable for people with uncontrolled high blood pressure or heart disease.
Melanotan IIAn unlicensed tanning peptide with sexual side effects.
- What it is
- Melanotan II activates several melanocortin receptors, darkening skin and also increasing sexual arousal. Bremelanotide was developed from it.
- What the evidence shows
- It does darken skin and can cause erections. There are no controlled trials supporting safe use.
- What to watch for
- Nausea, flushing, darkening and changes in moles, and case reports of melanoma.
OxytocinPitocin, SyntocinonThe bonding hormone, released during touch, sex and childbirth.
- What it is
- Oxytocin acts both as a hormone in the body and as a signal in the brain linked to trust, bonding and the sexual response, including orgasm.
- What the evidence shows
- Well established in childbirth. Studies of nasal oxytocin for social or sexual function have produced inconsistent results.
- What to watch for
- Nasal use in research is generally well tolerated in the short term. Long-term effects are unknown.
Sleep, immune and longevity
Sleep, immune function and cellular ageing.
DSIPDelta sleep-inducing peptideA peptide first isolated from sleeping animals.
- What it is
- DSIP was discovered in the 1970s in the blood of rabbits in induced deep sleep. Its natural role in humans is still not clearly understood.
- What the evidence shows
- Small human studies from the 1980s gave mixed results for sleep. No modern controlled trials exist.
- What to watch for
- Evidence is low quality and largely decades old.
EpitalonEpithalonA short synthetic peptide studied in Russia for ageing.
- What it is
- Epitalon is a four-amino-acid peptide based on an extract of the pineal gland. Lab studies suggest it may influence telomerase, the enzyme that maintains chromosome ends.
- What the evidence shows
- Evidence comes mostly from animal and cell studies plus a small number of older Russian human studies. No independent controlled trials exist.
- What to watch for
- Long-term human safety is unknown.
Thymosin alpha-1ThymalfasinAn immune-regulating peptide from the thymus.
- What it is
- Thymosin alpha-1 helps mature and direct T-cells, the immune cells that coordinate responses to infection. It is made by the thymus, which shrinks with age.
- What the evidence shows
- Clinical use in hepatitis and as an add-on in some infections and cancers, with mixed trial results. Little evidence in healthy people.
- What to watch for
- Generally well tolerated in clinical use.
GlutathioneThe body's main internal antioxidant, a three-amino-acid peptide.
- What it is
- Glutathione neutralises reactive molecules and helps the liver process toxins. The body makes its own from cysteine, glycine and glutamate.
- What the evidence shows
- Oral supplements may raise blood levels modestly. IV use is popular in clinics, but evidence for wellness or skin benefits is weak.
- What to watch for
- Generally well tolerated. IV infusions carry the usual risks of any infusion.
Hormones and PEDs
Testosterone, growth hormone, anabolic steroids and the medicines commonly used alongside them.
Androgens and growth hormone
Testosterone, growth hormone and the anabolic steroids derived from or related to them.
TestosteroneEnanthate, cypionate, undecanoate; gels and pelletsThe main male sex hormone, and the basis of testosterone replacement therapy.
- What it is
- Testosterone drives libido, muscle, bone density, red blood cell production and mood. It is given by injection, gel or pellet, either to restore low levels or, at higher amounts, for performance.
- What the evidence shows
- In men with genuinely low testosterone, replacement improves sexual function, mood, bone density and lean mass. A large 2023 trial found no increase in major heart events in men treated for low testosterone. Benefits in men with normal levels are less clear.
- What to watch for
- Raises haematocrit (blood thickness), shuts down the body's own production and usually reduces sperm count, and can raise oestrogen. Regular blood work covering haematocrit, oestradiol, lipids and PSA is essential.
SomatropinRecombinant human growth hormone (rhGH)Growth hormone itself, made in the lab.
- What it is
- Somatropin is identical to the growth hormone the pituitary makes. Rather than prompting the body to release more, it supplies the hormone directly, which overrides the body's own pulses.
- What the evidence shows
- Strong evidence of benefit in true deficiency. In healthy adults, studies show more lean mass, much of it water, without clear gains in strength or performance.
- What to watch for
- Joint pain, fluid retention, carpal tunnel symptoms and insulin resistance. IGF-1 and blood sugar should be monitored.
NandroloneNandrolone decanoate, DecaAn anabolic steroid known for muscle and joint-related use.
- What it is
- Nandrolone is a modified form of testosterone with strong muscle-building effects and weaker effects on hair and prostate. It has been used medically for anaemia and muscle wasting.
- What the evidence shows
- Trials in wasting conditions and kidney disease show gains in lean mass. Claims of joint benefit come mostly from anecdote rather than controlled studies.
- What to watch for
- Long-lasting suppression of natural testosterone, sexual side effects linked to prolactin, lower HDL cholesterol and strain on heart structure.
OxandroloneAnavarA mild oral anabolic steroid used to help regain weight after severe illness.
- What it is
- Oxandrolone is a pill-form steroid derived from DHT. It has been used to help people regain weight and muscle after burns, surgery or serious illness.
- What the evidence shows
- Good evidence for preserving muscle after severe burns. Less studied in healthy men.
- What to watch for
- Liver strain, a marked drop in HDL cholesterol and suppression of natural testosterone, even at modest amounts.
TrenboloneTrenA very potent veterinary steroid developed to build muscle in cattle.
- What it is
- Trenbolone is a modified nandrolone that binds the androgen receptor very strongly and does not convert to oestrogen. It was developed for livestock and has never been tested in human trials.
- What the evidence shows
- No human research. Its reputation for rapid muscle and strength gains comes from anecdote.
- What to watch for
- Severe drops in HDL cholesterol, raised blood pressure, poor sleep, night sweats, mood changes including aggression, and strong suppression of natural testosterone.
StanozololWinstrolAn oral or injectable DHT-derived steroid.
- What it is
- Stanozolol is a DHT-based steroid that does not convert to oestrogen. It has been used medically for hereditary angioedema, a rare swelling condition.
- What the evidence shows
- Medical evidence centres on angioedema. Performance claims are anecdotal.
- What to watch for
- Liver strain, one of the sharpest drops in HDL cholesterol of any steroid, and suppression of natural testosterone.
Supporting medicines
Compounds used to manage oestrogen or restart natural testosterone production.
EnclomipheneA pill that raises the body's own testosterone without suppressing fertility.
- What it is
- Enclomiphene blocks oestrogen's feedback signal in the brain, so the pituitary releases more LH and FSH. The testes then make more testosterone and sperm on their own.
- What the evidence shows
- Trials show it raises testosterone into the normal range while preserving sperm count, unlike testosterone therapy.
- What to watch for
- Visual disturbances, mood changes and raised oestradiol. Does not work if the testes themselves are failing.
AnastrozoleArimidexAn aromatase inhibitor that lowers oestrogen.
- What it is
- Anastrozole blocks aromatase, the enzyme that converts testosterone into oestradiol. It is sometimes added to testosterone therapy when oestradiol climbs.
- What the evidence shows
- It reliably lowers oestradiol. Whether routine use alongside testosterone therapy improves outcomes is debated.
- What to watch for
- Pushing oestradiol too low harms bone density, libido, joints, mood and cholesterol. It should only be guided by blood work.
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