What are peptides, in plain English?
A peptide is a chain of two or more amino acids, the small molecules your body joins together to build proteins (NCI). Picture beads on a string, where each bead is one amino acid.
Make the string long enough and you have a protein. The National Human Genome Research Institute puts peptides at about 2 to 50 amino acids, and says the proteins your cells make are built from one or more longer chains (NHGRI).
FDA draws a sharper line for regulation. Under its rules, a chain of more than 40 amino acids counts as a protein (21 CFR 600.3). That line moves real products: on March 23, 2020, insulin products switched from FDA's drug pathway to its biologics pathway under that protein definition (FDA).
Your body makes its own peptides. GLP-1 (glucagon-like peptide-1) is one. Semaglutide's prescribing label calls it "a physiological regulator of appetite and caloric intake" (Wegovy label, DailyMed). Keep GLP-1 in mind, because it explains why you're hearing the word everywhere.
Why are people taking peptides now? Blame GLP-1 medicines
Semaglutide, sold as Ozempic and Wegovy, is a peptide. Its label says the drug's "peptide backbone is produced by yeast fermentation" and that it shares 94% of its sequence with human GLP-1 (Wegovy label).
FDA approved Wegovy for chronic weight management on June 4, 2021 (FDA approval letter). In the STEP 1 trial, adults on semaglutide lost 14.9% of their body weight on average over 68 weeks, against 2.4% on placebo. Both groups also got a lifestyle program (PMID 33567185).
Results like that turned "peptide" into a kitchen-table word. In Google Trends, US interest in "what are peptides" roughly doubled between October 2025 and September 2026. The fastest-rising related search over the year was "what are peptides and why are people taking them" (Google Trends).
The word now stretches from prescription pens to skincare jars to vials sold online as "research" products. Those are very different things, so the next section sorts them. For the head-to-head numbers on the two biggest weight-loss peptides, see semaglutide vs tirzepatide, and the weight management hub collects every related profile.
Approved medicine, trial drug or research chemical: the three kinds of peptide
Every peptide you hear about lands in one of three groups, and the group tells you most of what you need to know about the evidence.
1. FDA-approved medicine. The maker ran controlled human trials, and FDA reviewed them before approval. Semaglutide is the clearest example, and it is prescription-only. Approval covers the approved products, not copies. FDA says compounded versions "are not FDA approved," so the agency does not review them for safety, effectiveness or quality before they are sold (FDA).
2. Clinical-trial drug. The peptide is being tested in people but hasn't been approved. Retatrutide is one: Eli Lilly registered TRIUMPH-1, a phase 3 trial in adults with obesity or overweight, as NCT05929066. FDA says retatrutide has "not been found safe and effective for any condition" and cannot be used in compounding (FDA). Late-stage trials still fail. FDA's own figures put the share of drugs that get past phase 3 at about 25% to 30% (FDA).
Read this next Semaglutide evidence profile
3. "Research chemical." These are vials sold online labeled "research use only" or "not for human consumption." FDA looks past the label. In an August 24, 2026 warning letter to Royal Peptides LLC, FDA said evidence on the company's website showed its products were "intended to be drugs for human use," and pointed to the bacteriostatic water, "peptide guide" and "peptide calculator" sold alongside them (FDA warning letter). FDA calls products like these "of unknown quality" and says they "may be harmful to their health" (FDA).
BPC-157 shows where the third group leaves you. FDA lists it among bulk drug substances that may present significant safety risks in compounding, with "no, or only limited, safety-related information for the proposed routes of administration" (FDA). Its approval status by country is on our BPC-157 evidence profile.
Read this next: BPC-157 human trials: every human study so far, and why none is a published randomized trial
How to read a peptide claim: human trials vs animal and lab data
Before you trust a study cited for a peptide, ask four questions.
Who was studied: people, animals or cells? Results in rats or cell cultures tell researchers where to look next. They don't show that a peptide works in people. For BPC-157, our standard wording applies: Most of the research so far comes from laboratory and animal studies. That does not tell us whether it works in people.
Animal findings about harm don't settle the human question either. Semaglutide carries a boxed warning because it caused thyroid C-cell tumors in rodents. Its label says it is "unknown" whether it causes these tumors in humans, because their human relevance "has not been determined" (Wegovy label).
Was there a comparison group? A randomized trial puts some people on the peptide and others on placebo, chosen by chance. STEP 1's 14.9% only means something next to the placebo group's 2.4%. A testimonial has no comparison, so it can't separate the peptide from diet, time or luck.
How many people, in what phase? FDA describes phase 1 trials as 20 to 100 people focused on safety and dosage, and phase 3 trials as 300 to 3,000 people. About 70% of drugs move past phase 1, and about 33% move past phase 2 (FDA). A small early study is a reason to keep testing, and only that.
Is there a published result, or only a registration? A ClinicalTrials.gov entry shows a trial was planned and who runs it. Results come later, if ever. A registry number on a sales page proves a trial exists and nothing more.
Our methods page turns these questions into grades, and peptides ranked by evidence applies them to every profile on the site. Semaglutide sits at the top with an A. BPC-157 sits at the bottom with an F, because no randomized controlled trial of it has been published.
Where to start on Straight Up Peptides
Pick the path that matches what brought you here.
- You heard about Ozempic or Wegovy. The semaglutide evidence profile covers the trials, the side effects and the status in the US and Canada, with every claim cited.
- You heard about BPC-157 in a gym or a group chat. The BPC-157 evidence profile separates the animal work from the small human record.
- You want to compare two compounds. The compare tool lines up measured outcomes side by side and flags where studies are too different to match.
- You want the whole field at a glance. The evidence rankings order every profile by the strength of its human evidence.
Common questions about peptides
Are peptides the same as proteins?
They're made of the same building blocks, amino acids, but peptides are shorter. NHGRI puts peptides at about 2 to 50 amino acids (NHGRI). For regulation, FDA treats any chain of more than 40 amino acids as a protein (21 CFR 600.3).
Is semaglutide a peptide?
Yes. The Wegovy label describes semaglutide as a GLP-1 analogue with a "peptide backbone" made by yeast fermentation, sharing 94% of its sequence with human GLP-1 (Wegovy label).
Are peptides FDA approved?
Some are. FDA approved semaglutide as Wegovy for chronic weight management on June 4, 2021 (FDA). Approval belongs to a specific product, though. FDA has warned companies selling semaglutide, tirzepatide, retatrutide, survodutide or mazdutide falsely labeled "for research purposes" (FDA).
Are peptides safe?
It depends on which peptide and which product. For approved semaglutide, the side effects are measured: in STEP 1, nausea and diarrhea were the most common, and 4.5% of people on semaglutide stopped because of stomach and gut side effects, against 0.8% on placebo (PMID 33567185). For BPC-157, FDA says it lacks the information to know whether it would cause harm in humans (FDA). A licensed clinician is the right person to weigh any specific product for you.
Are peptides steroids?
No. Steroids are a group of lipids (fats) with a particular chemical structure, a group that includes sex hormones and cholesterol (NCI). Peptides are chains of amino acids (NCI). They are two different classes of molecule.
Sources
- National Cancer Institute. Definition of peptide. NCI Dictionary: peptide
- National Cancer Institute. Definition of steroid. NCI Dictionary: steroid
- National Human Genome Research Institute. Peptide (glossary, updated October 8, 2026). NHGRI glossary: Peptide
- 21 CFR 600.3(h)(6), definition of protein. 21 CFR 600.3 protein definition
- FDA. FDA works to ensure smooth regulatory transition of insulin and other biological products (February 20, 2020). FDA insulin biologics transition
- Wegovy (semaglutide) prescribing information, Novo Nordisk, revised 06/2026. DailyMed: Wegovy label
- FDA. Wegovy approval package, NDA 215256, approval date June 4, 2021. FDA Wegovy approval letter (PDF)
- Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PMID 33567185. DOI 10.1056/NEJMoa2032183. PubMed: STEP 1 (PMID 33567185)
- FDA. FDA's concerns with unapproved GLP-1 drugs used for weight loss. FDA: unapproved GLP-1 drugs
- ClinicalTrials.gov. NCT05929066, TRIUMPH-1 (retatrutide, phase 3, Eli Lilly). ClinicalTrials.gov: NCT05929066
- FDA. Step 3: Clinical Research. FDA: clinical research phases
- FDA. Warning letter to Royal Peptides LLC, MARCS-CMS 734884, August 24, 2026. FDA warning letter: Royal Peptides LLC
- FDA. Certain bulk drug substances for use in compounding that may present significant safety risks (content current as of 04/22/2026). FDA: bulk substances with safety risks
- Google Trends, United States, past 12 months (2025-10-05 to 2026-10-04), pulled October 9, 2026. Relative interest only, not search volume. Google Trends: what are peptides
