RESEARCH PEPTIDE FUNDAMENTALS / FAQ
Straight Answers, No Hedging
The questions readers most often bring to these five research peptides, answered directly from the cited literature.
What does BPC-157 do in the body?
In animal models, BPC-157 promotes tissue repair, chiefly by driving angiogenesis — new blood-vessel growth — through up-regulation and internalization of the VEGFR2 receptor and downstream Akt-eNOS signaling [4]. That mechanism underlies its studied effects on gut-lining healing, tendon and ligament repair, and ischemic-muscle recovery in rats and mice. In the one published human study, two adults given intravenous BPC-157 showed no adverse effects and no changes to major safety markers, but that pilot tested tolerability, not what the compound actually does in a person [1]. Everything beyond that is animal data, not confirmed human effect.
Is BPC-157 a growth hormone?
No. BPC-157 is not a growth hormone and doesn't act as one. Its reported link to growth signaling is narrower: in cultured tendon fibroblasts, it appears to sensitize the growth-hormone receptor, meaning it may make tendon cells more responsive to growth-hormone signaling already present — not that BPC-157 itself functions as a growth hormone. This is a mechanistic, cell-culture-level finding, not evidence that BPC-157 raises growth-hormone levels or acts like one in a whole organism.
Does BPC-157 damage the liver?
The one published human study — a small IV safety pilot in two adults — found no measurable changes in hepatic (liver) biomarkers [1]. That is reassuring but extremely limited: two people is nowhere near enough to rule out a liver-safety signal. No large human safety trial has been run, and a 2025 review of the field explicitly states that rigorous, large-scale human trials are lacking [2]. The honest answer is that liver safety in humans hasn't been adequately studied either way.
What is KPV peptide?
KPV is a three-amino-acid tripeptide (lysine-proline-valine) corresponding to the tail end of the hormone alpha-MSH. It retains alpha-MSH's anti-inflammatory signaling while dropping its pigment-related activity, which is why it's studied specifically for gut inflammation rather than skin pigmentation [8][10]. It has never been tested in a published human clinical trial — the entire evidence base is cell culture and mouse colitis models.
What does KPV peptide do?
In preclinical models, KPV suppresses NF-kB and MAP-kinase inflammatory signaling and reduces output of pro-inflammatory cytokines, entering intestinal cells via the PepT1 transporter, which is upregulated in inflamed gut tissue [8]. In mouse colitis models this has translated to earlier recovery, lower tissue-damage markers, and reduced inflammatory infiltrate [9]. None of this has been confirmed in a human trial.
What is NAD supplement used for?
NAD+ supplements — usually precursor forms like NMN or NR rather than NAD+ itself — are marketed for cellular energy and anti-aging support, on the basis that NAD+ levels decline with age and fuel enzymes involved in DNA repair and metabolic regulation [14]. Human trials confirm these precursors reliably raise blood NAD+ in a dose-dependent way [12][15], and one trial found a measurable improvement in muscle insulin sensitivity [13]. What the trials do not yet confirm is a broader anti-aging or disease-prevention benefit; a 2025 review calls that evidence still limited [11].
What is the downside of taking NAD+?
For oral precursor forms (NMN, NR) at studied doses, trial data show a favorable safety profile with no significant excess of adverse events versus placebo [12][15]. The real downside risk sits with the IV/injectable route: compounded NAD+ infusions are not FDA-approved products, have been linked to discomfort when infused too quickly, and the FDA issued a Class I recall for one compounded NAD+ injection over bacterial endotoxin contamination. There's also a theoretical, unresolved concern that boosting NAD+ could support the growth of existing cancer cells, since NAD+ fuels proliferating cells generally.
Is it safe to take NAD daily?
Trial data on NMN and NR precursors at studied daily doses — up to 900 mg/day for NMN and 1000 mg/day for NR — found them well tolerated over the trial periods (60 and 56 days respectively), with no significant difference in adverse events from placebo [12][15]. That's evidence for daily oral precursor use within those specific trial windows, not a blanket safety guarantee for any product, dose, or duration outside what was studied — and it says nothing about the safety of daily IV NAD+ infusions specifically, which carry separate product-quality and infusion-rate risks.
Does NAD cause weight gain?
None of the cited human trials of NAD+ precursors reported weight gain as a finding. The 60-day NMN trial reported improved walking distance and no increase in a biological-age measure, with no mention of weight change as an outcome [12]; the muscle-insulin-sensitivity trial found no change in body composition [13]. There's no published evidence linking NAD+ supplementation to weight gain.
What does retatrutide do?
Retatrutide activates three receptors at once — GLP-1, GIP, and glucagon — combining appetite suppression and improved insulin secretion (from the first two) with increased energy expenditure (from the glucagon arm) [16][17]. In a 48-week Phase 2 trial, the 12 mg dose produced -24.2% average body-weight loss versus -2.1% with placebo, the largest figure reported for any incretin-class compound tested to date [19].
Is retatrutide FDA approved?
No. Retatrutide is not approved by the FDA or any other regulator as of mid-2026. It remains in Phase 3 trials (the TRIUMPH program), and every efficacy and safety figure available comes from Phase 1 and Phase 2 studies [16][19][20]. It is legally available only to participants enrolled in registered clinical trials; the FDA issued more than 50 warning letters to vendors selling it outside that context in 2025.
What is tirzepatide?
Tirzepatide is a 39-amino-acid synthetic peptide that activates two receptors at once — GIP and GLP-1 — earning it the label "twincretin" or dual incretin agonist [26]. It's FDA-approved for type 2 diabetes, chronic weight management, and moderate-to-severe obstructive sleep apnea in adults with obesity [22]. It's the only compound on this desk with a mature, multi-trial approval record.
What is tirzepatide used for?
Its FDA-approved uses are type 2 diabetes mellitus (approved 2022), chronic weight management in adults with obesity or overweight plus a weight-related condition (approved 2023), and moderate-to-severe obstructive sleep apnea in adults with obesity [22]. In trials, it also outperformed semaglutide head-to-head on both weight loss (-20.2% versus -13.7% over 72 weeks) [21] and HbA1c reduction in type 2 diabetes [25]. It's a prescription medicine, not available for self-directed use outside a licensed prescriber relationship.
How do these five compounds compare on safety, overall?
They don't compare cleanly, because they aren't at the same evidence stage. Tirzepatide has the most thoroughly documented safety profile — including real, quantified risks like gallbladder disease [23] — precisely because it has the most human data. Retatrutide's documented risks (dose-dependent heart-rate increase, GI intolerance) come from real Phase 2 trials, but long-term outcomes remain unknown [19]. NAD+ precursors look safe within the doses and durations actually tested [12][15], though the IV form carries separate, real contamination risk. BPC-157's safety case rests on one two-person pilot plus rodent data [1][2] — thin, not damning. KPV has no human safety data of any kind to evaluate. More documented risk on this page generally signals more human study, not more danger — the compound with zero red flags on this desk (KPV) is also the one with zero human evidence, not the safest one.