Peptides Explained: What Each One Actually Does, and What the Evidence Shows

"Peptides" isn't one thing. It's a category that includes an FDA-approved libido treatment and compounds with almost no independent human data at all. Here's what the evidence actually shows for the ones we see most, the same lineup available through our EllieMD referral.

MK Wellness InsightsFounded by Danielle Cordova, Cypress, TX

People talk about "peptides" like it's a single category with a single risk profile. It isn't. PT-141 is a peptide, and it's an FDA-approved drug. Epitalon is a peptide, and the human evidence for it is telomere-lengthening data in cultured cells and animal studies, not human trials. Lumping all of them together, good or bad, real or sketchy, misses the actual picture. Here's what the evidence shows for the specific compounds available through our EllieMD referral.

Tissue Repair: KLOW

KLOW is a four-peptide blend, BPC-157, TB-500, GHK-Cu, and KPV, combined for recovery, gut health, skin, and tissue repair. Each component has a different mechanism and a different evidence base, worth knowing individually rather than treating the blend as one thing.

BPC-157, a synthetic pentadecapeptide originally derived from a protein in gastric juice, has shown real effects in animal models: supporting angiogenesis, collagen synthesis, and fibroblast activity, including a measurable increase in growth hormone receptor expression in tendon fibroblasts. Human data is limited to small pilot studies.

TB-500 (Thymosin Beta-4) binds to G-actin, a protein involved in cell migration, directing it toward tissue repair and new blood vessel growth. It has more human data than BPC-157, Phase II trials have shown accelerated wound closure in chronic and acute skin wounds, though that evidence is concentrated in wound healing specifically. It's currently under FDA Pharmacy Compounding Advisory Committee review for the 503A bulk substances list.

GHK-Cu, a naturally occurring copper-binding peptide, has the strongest published evidence of the four. It up- and down-regulates a substantial number of human genes and has documented effects on collagen synthesis, skin firmness, and wound healing in published studies, the best-established evidence base in this entire blend.

KPV, the C-terminal fragment of a naturally occurring hormone, works through a different anti-inflammatory pathway than the others, direct inhibition of NF-kB signaling rather than receptor binding, and is generally studied for gut and inflammatory applications.

Growth Hormone: Sermorelin

Sermorelin stimulates the pituitary gland to release the body's own growth hormone by mimicking GHRH, the hormone that naturally signals that release. It has the most established regulatory history of any peptide on this list: it was actually FDA-approved for pediatric growth hormone deficiency before the branded version was discontinued for commercial, not safety, reasons. It remains available through licensed compounding pharmacies in both injection and capsule form.

Cognitive & Mood: Semax, Selank, and Dihexa

Semax and Selank both originated in Soviet and post-Soviet Russian pharmacology in the 1980s and 90s, and both are registered drugs in Russia today, Semax for cerebrovascular and neurological use, Selank as an anxiolytic. Semax works by upregulating BDNF and NGF, signaling proteins involved in neuronal survival and synaptic plasticity. Selank is a synthetic analog of a naturally occurring peptide that modulates GABA-A receptor activity, the same general system targeted by anti-anxiety medications. Neither has FDA approval, and neither has been evaluated in a randomized controlled trial under Western regulatory standards. Worth noting: Semax was removed from the FDA's Category 2 restricted compounding list in 2026 and is scheduled for further review, a regulatory picture that's actively moving, not settled.

Dihexa is a small, orally bioavailable compound derived from angiotensin IV, developed at Washington State University specifically to be more stable and brain-penetrant than earlier neurotrophic research compounds. Published preclinical research describes cognitive-enhancing activity well beyond what was achievable with earlier approaches in the same category. Like Semax and Selank, this is compelling mechanism and animal data without human clinical trials behind it yet.

Longevity: Epitalon

Epitalon is a synthetic four-amino-acid peptide modeled on epithalamin, a pineal gland extract, developed by Russian researcher Vladimir Khavinson in the 1980s. Its two proposed mechanisms are telomerase activation, potentially slowing telomere shortening, and pineal gland regulation, restoring melatonin secretion and circadian rhythm. Laboratory research has shown Epitalon inducing telomerase activity and measurable telomere elongation in human fetal fibroblast cultures, and animal research has shown increased melatonin synthesis and extended lifespan. Whether synthetic Epitalon produces the same effect in a living human body that it produces in a petri dish is, honestly, still an open question in the research. The mechanism is genuinely interesting. Treat the anti-aging framing with appropriate skepticism until human trials catch up to the cell-culture data.

Immune Support: Thymosin Alpha-1

Thymosin Alpha-1 has a well-characterized immunomodulatory mechanism: it enhances T lymphocyte function, modulates interleukin-2 production, stimulates interferon-gamma, and increases natural killer cell activity. It has genuine pharmaceutical history outside the United States, prescribed for immune support in certain conditions, though it isn't FDA-approved here.

Sexual Health: PT-141

PT-141 (bremelanotide), marketed as Vyleesi, is the one clear outlier on this list: it's actually FDA-approved, cleared in 2019 for hypoactive sexual desire disorder in premenopausal women. It works on brain pathways involved in desire rather than blood flow, a different mechanism than most other sexual health treatments. It's not approved for men, and use in men is off-label.

Why the Evidence Quality Varies So Much

Look back across this list and a real spread shows up: an FDA-approved drug (PT-141), a peptide with genuine prior FDA approval history (Sermorelin), a peptide with real Phase II human trial data in a narrow application (TB-500), a peptide with the strongest published mechanistic data in its blend (GHK-Cu), Russian-registered drugs with no Western regulatory equivalent (Semax, Selank), and compounds where the most compelling evidence is still in cell cultures and animal models (Epitalon, BPC-157, Dihexa). None of that is a reason to dismiss the newer compounds, the mechanisms are frequently plausible and the preclinical data is often genuinely strong. It's a reason to want a provider who can tell you exactly which category something falls into before you use it, rather than a label that just says "research use only."

That's the same conclusion we reached writing about sourcing and dosing: the compound matters less than who is evaluating you, how it's sourced, and how the dose is determined.

Where MK Wellness Fits

We don't source, dispense, or administer peptides at MK Wellness. For clients who want to explore this category with an actual medical evaluation, we refer to EllieMD, a telehealth platform with licensed physicians who review your health history before anything is prescribed.

MK Wellness services are non-medical and not intended to diagnose, treat, cure, or prevent any condition. This article is general educational information, not medical advice, and is not an endorsement of any specific peptide's safety or efficacy for any use. Peptide therapy requires evaluation and prescription by a licensed medical provider.

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