# Research Peptide FAQ — BPC-157, KPV, NAD+, Retatrutide, Tirzepatide — Research Peptides US > Straight, citation-anchored answers to the questions people actually ask about BPC-157, KPV, NAD+, retatrutide, and tirzepatide. 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. --- A no-nonsense literature rundown on research peptides — straight evidence, no sales, no dosing advice.