Peptides for men’s health

What’s been tested for testosterone, fertility and erections, and what guidelines recommend first.

The short answer

Testosterone is a steroid hormone, not a peptide. For diagnosed low testosterone, the Endocrine Society recommends testosterone therapy after two low morning blood tests and matching symptoms, and recommends against it for men planning a pregnancy soon, because it suppresses sperm production.

Among peptides, hCG is approved for low testosterone caused by a pituitary problem and can start sperm production; in small studies it also kept testicular testosterone up in men on testosterone. Kisspeptin raised LH and testosterone in short studies. Claims that peptides restart natural testosterone after steroid cycles rest on user reports.

For erections, no peptide is approved in the US. VIP with phentolamine is licensed in the UK and parts of Europe as an injection into the penis, and PT-141 and melanotan II were tested only in small trials.

20 uses on this site’s compound pages: 2 on labels, 9 tested in people, 1 in animals only, 8 claims only.

What guidelines recommend

Low testosterone: testosterone therapy for men with symptoms and consistently low morning levels, after looking for the cause (Endocrine Society, 2018).
Erection problems: pills such as sildenafil and tadalafil, injections into the penis, vacuum devices and implants can all be first-line, chosen together with a clinician (American Urological Association, 2018).

On a label 2

Approved uses, from a product label somewhere in the world.

hCGApproved drug: LabelLow testosterone from a pituitary cause. Approved for selected men with hypogonadotropic hypogonadism. Gonadotropin treatment (hCG, often with FSH) started sperm production in 75% of men with none, in a 2014 meta-analysis of 44 studies.
VIPApproved drug: LabelErectile dysfunction, with phentolamine. Invicorp, injected into the penis, is licensed in the UK and several European countries. In label trials of 343 men, 73–74% of injections gave an erection suitable for sex vs 12–13% on placebo.

Tested in people 9

Studied in people, whatever the result: some worked, many didn’t or are unproven.

L-CarnitineApproved drug: TrialSperm quality in male infertility. Mixed: a meta-analysis of 8 oral trials found better sperm movement and shape, but no clear rise in pregnancy rates.
GlutathioneApproved drug: TrialMale infertility (sperm quality). Small trial: in 20 men, muscle injections every other day for 2 months improved sperm movement and shape vs placebo in a crossover design. Pregnancy outcomes weren’t reported.
VesugenPreclinical: TrialErectile dysfunction from narrowed arteries. Unproven: a Russian report on 41 men says penile artery blood flow improved after a Vesugen course; it compared before and after only and gives no numbers in the abstract.
Melanotan 2Human studies: TrialErectile dysfunction. Positive in two tiny trials but never approved: single injections produced erections in 8 of 10 men (1998) and after 12 of 19 doses vs 1 of 21 on placebo (2000), with frequent nausea.
hCGApproved drug: TrialProtecting fertility on testosterone therapy. Small studies only: in 29 healthy men on testosterone, 250–500 IU every other day kept testicular testosterone near or above baseline for 3 weeks. Sperm data come from a 26-man records review.
Kisspeptin-10Human studies: TrialRaising LH and testosterone in men. Shown short term: IV doses raised LH within 30–45 minutes, and a 22.5-hour infusion raised testosterone from 16.6 to 24.0 nmol/L. Daily 8-hour under-the-skin infusions kept hormones up for 12 days.
Kisspeptin-10Human studies: TrialLow testosterone (secondary hypogonadism). Unproven: in 12 men with type 2 diabetes and low testosterone, an 11-hour IV infusion raised testosterone from 8.5 to 11.4 nmol/L. FDA judged the evidence insufficient for treatment.
PT-141Approved drug: TrialErectile dysfunction. Unproven: small lab studies found nasal or injected doses caused erections; one 342-man nasal trial reported benefit, but that paper has a 2023 expression of concern. Not approved for men.
GonadorelinApproved drug: TrialFertility in men lacking GnRH. Partly positive: pump therapy started sperm production about 5 months sooner than hCG with hMG in a pooled analysis of 420 men; sperm counts and pregnancy rates didn’t differ significantly.

Seen only in animals 1

Results in animals or cells only. Most treatments tested in animals never reach approval for people.

FOXO4-DRIPreclinical: AnimalTestosterone and sperm in older men. Unproven in people: in naturally aged mice, it cleared senescent testosterone-making (Leydig) cells, eased the age-related drop in testosterone and improved sperm quality, in two studies from one Chinese university.

Claims without data 8

Promoted by sellers, clinics or users, with no study behind the claim.

ProstamaxPreclinical: No studyErectile function and libido. Unproven: no study has tested it for erections, libido or testosterone, in people or animals.
hCGApproved drug: CommunityRestarting testosterone after steroid cycles. Unproven: used during or after steroid cycles to restart natural testosterone; only case reports and reviews exist, no controlled trial. WADA bans hCG in male athletes.
Kisspeptin-10Human studies: CommunityRestarting testosterone after steroids. Unproven: used to try to restart natural testosterone, but no study has tested daily injections for this, and nonstop exposure blunted LH and FSH responses within 5 days.
PT-141Approved drug: CommunityLibido in men or after menopause. Unproven: users report it, but no published trial has tested it for low desire in men or in women after menopause, and the label excludes both groups.
GonadorelinApproved drug: CommunityProtecting the testes on testosterone therapy. Unproven: popular as an hCG substitute, but no trial has tested it with testosterone therapy. Each dose acts for minutes; the evidence comes from pumps pulsing every 90 minutes.
GonadorelinApproved drug: CommunityRestarting testosterone after steroids. Unproven: no study has tested injections for recovery after steroid use, and continuous or too-frequent exposure suppresses LH and FSH rather than raising them.
TriptorelinApproved drug: CommunityRestarting testosterone after steroid use. Unproven: some users inject a single small dose after a steroid cycle to try to restart their own testosterone. No study has tested this, and repeated or depot dosing shuts testosterone down instead.
TestagenPreclinical: No studyTestosterone, sperm and libido. Unproven: no published study has tested it on testosterone, sperm, libido or the testes, in animals or people. Its developers list male reproductive function but cite no such study.

Sexual health and fertility guide, hCG, Kisspeptin-10.

The same uses among all hormones, sex and reproduction: evidence map. Every condition, A to Z: conditions A to Z.

Sources: Bhasin et al., Endocrine Society testosterone therapy guideline (J Clin Endocrinol Metab 2018), PMID 29562364; Burnett et al., American Urological Association erectile dysfunction guideline (J Urol 2018), PMID 29746858; each compound’s answer from its own page, where its sources are listed.

By Vial Guide editorsLast reviewed October 7, 2026

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