# From Lab Compound to Licensed Drug > API Peptide — Research Peptide Fundamentals — API Peptide is a plain-English orientation to four of the most-studied research peptides — semaglutide, tirzepatide, tesamorelin, and BPC-157 — read as active pharmaceutical ingredients, from lab compound to licensed drug. **RESEARCH PEPTIDE FUNDAMENTALS** A cited, plain-English guide to four research peptides — semaglutide, tirzepatide, tesamorelin, and BPC-157 — that shows what each one actually is as an active pharmaceutical ingredient, and how far the published evidence for each one reaches. ### [Semaglutide](/semaglutide) ![Semaglutide research illustration](images/semaglutide.webp) A long-acting GLP-1 receptor agonist and the benchmark incretin drug — FDA-approved across diabetes, weight management, cardiovascular and kidney indications. ### [Tirzepatide](/tirzepatide) ![Tirzepatide research illustration](images/tirzepatide.webp) A dual GIP/GLP-1 receptor agonist that outperformed semaglutide head-to-head — the first approved twincretin. ### [Tesamorelin](/tesamorelin) ![Tesamorelin research illustration](images/tesamorelin.webp) A GHRH analogue approved for one specific indication — HIV-associated lipodystrophy — and a useful case study in how narrow an approval can be. ### [BPC-157](/bpc-157) ![BPC-157 research illustration](images/bpc-157.webp) A gastric pentadecapeptide with a large animal literature and almost no human data — never approved, and the clearest illustration of the API-to-drug gap. ## The short version An active pharmaceutical ingredient, or API, is the molecule that actually does the work inside a medicine — everything else in a pill or vial is packaging, stabilizer, or delivery vehicle. This site looks at four peptide APIs side by side: **semaglutide** and **tirzepatide**, both approved prescription medicines; **tesamorelin**, approved but only for one narrow condition; and **BPC-157**, a peptide with decades of animal research behind it that has never been approved as a drug at all. Walking these four through the same lens — what the molecule is, how it reached (or didn't reach) approval, and what the human evidence actually shows — makes the *drug development gap* visible. A molecule having a receptor, a mechanism, and even promising animal data is not the same as it being a licensed medicine. Regulatory approval requires large controlled human trials, and that bar is why these four compounds sit at such different points on the same road. ## Peptides as active pharmaceutical ingredients Every peptide covered here began the same way: as a synthetic analogue of a naturally occurring signaling molecule, engineered to be more stable, longer-acting, or more selective than the body's own version. Semaglutide and tirzepatide are both engineered analogues of gut incretin hormones (GLP-1, and GLP-1 plus GIP), modified with fatty-acid side chains that bind albumin and stretch a two-minute native half-life out to roughly a week. Tesamorelin is an engineered analogue of growth hormone-releasing hormone (GHRH), stabilized against enzymatic breakdown. BPC-157 is derived from a fragment of a human gastric-juice protein. What separates these APIs from one another is not chemistry but *evidence and regulatory status*. Semaglutide and tirzepatide each carry multiple large randomized controlled trials and multiple FDA approvals. Tesamorelin carries one FDA approval, tightly scoped to abdominal fat reduction in HIV-associated lipodystrophy — its manufacturer never sought, and does not have, approval for any broader use. BPC-157 has essentially no controlled human trial data; a 2025 narrative review notes only three small human pilot studies exist [18]. None of that means BPC-157's animal findings are false — it means the API-to-licensed-drug journey for BPC-157 has not been made, and readers should treat that difference as load-bearing, not cosmetic. ## What are research peptides? Peptides are short chains of amino acids — the same building blocks as proteins, just far smaller. Because so many of the body's own signaling molecules (hormones, growth factors, neurotransmitter modulators) are themselves peptides, synthetic peptide APIs can often slot directly into existing biological receptors. That is the shared mechanism across everything on this site: each of the four compounds here activates a receptor system that already exists in the human body — the GLP-1/GIP receptors, the GHRH receptor, or (in BPC-157's case) a proposed VEGFR2-linked pathway. 'Research peptide' is a supply-chain label, not a scientific one. It describes material sold by laboratory-supply vendors for non-clinical research use, before or instead of a formal drug-development and approval pathway. Semaglutide and tirzepatide are both available as research peptides from some suppliers even though they are also FDA-approved medicines sold under prescription; tesamorelin's approved indication is narrow enough that most use of the API outside that indication is off-label; BPC-157 is sold as a research chemical only, with no approved human indication anywhere. This site does not sell any of these compounds and does not recommend a dose for a person to take — it reports what the published research and regulatory record actually say. --- API Peptide traces each compound from lab molecule to (sometimes) licensed drug and back only as far as the citation trail actually goes — an editorial desk, not a clinic, a pharmacy, or a source.