--- title: "How Are Peptides Made? Synthesis, Purity & Quality" description: "How peptides are made: extraction, recombinant bacteria and solid-phase peptide synthesis, step by step, plus what purity means and why testing a vial matters." canonical: "https://www.vitalsvault.com/peptides/how-are-peptides-made" last-updated: 2026-08-22 --- # How Are Peptides Made? Synthesis, Purity & Quality > How peptides are made: extraction, recombinant bacteria and solid-phase peptide synthesis, step by step, plus what purity means and why testing a vial matters. ![A chemist in her late thirties stands at a bright laboratory bench holding a glass flask at chest height, looking at it calmly, safety glasses,…](https://www.vitalsvault.com/_next/image?url=%2Fpublic-v3%2Fshoot%2Fpeptides%2Fpep101-made.webp&w=3840&q=75&dpl=shadow-production-f0162cb4d465-40992538108-1) Peptide Guide · Explainer # How are peptides made? Every synthetic peptide is built one amino acid at a time, in a fixed order, and every step has a small chance of going wrong. How chemists manage that chance decides what ends up in the vial. [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist)[Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) Free to join · One email when peptide care opens · Most lab results in 3–5 business days ## The answer, in short Most peptides today are made by solid-phase peptide synthesis. Chemists anchor the first amino acid to a tiny resin bead and add the rest one at a time, washing away excess reagents after each step. The finished chain is cut off the bead, purified by chromatography and freeze-dried into powder. Some larger peptides, like insulin, are made by engineered microbes instead. Medically reviewed by [Robert Lufkin, MD (opens in a new tab)](https://www.robertlufkinmd.com/) Chief Medical Officer, Vitals Vault · Updated October 29, 2026 · 15 sources ## A protein built on a grain of sand In the late 1950s, a young chemist at the Rockefeller Institute named Bruce Merrifield was making peptides the slow way. Each time he added an amino acid to a growing chain, he had to purify the product before he could add the next one. A short peptide could take months, and much of the material was lost along the way. His idea was almost comically simple. What if the growing chain were tied to something solid, a tiny insoluble bead, so that every leftover chemical could just be washed off? Add an amino acid, rinse the beads, add the next, rinse again. The chain never leaves the bead until the end, so there is nothing to fish out of solution between steps. Merrifield called it solid-phase synthesis. It made peptide chemistry fast enough to automate, earned him the Nobel Prize in Chemistry, and it is still how most peptides you will read about in this guide are made. When chemists today build a peptide drug by the ton, they are using a refined version of the same rinse-and-repeat cycle.[1](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-merrifield-1986)[3](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-behrendt-2016) ## The three ways to make a peptide There are three basic ways to get a peptide into a vial, and they produce quite different products. Knowing which one you are looking at answers a surprising number of questions about purity and safety.[5](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-goeddel-1979)[3](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-behrendt-2016) - 01 ### Extract it from tissue The oldest route. For decades, insulin came from the pancreases of pigs and cows. Cerebrolysin is still made this way, by digesting pig brain proteins into a mixture of small peptides and amino acids. One analysis of an internet-bought sample found 638 distinct peptides in it, which is why it has no single defined active ingredient.[7](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-gevaert-2015)[5](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-goeddel-1979) - 02 ### Grow it in microbes In 1979, a team at Genentech and City of Hope wrote synthetic genes for the two chains of human insulin, put them into E. coli bacteria and got the bacteria to make them. The chains were purified, combined and folded into insulin. Engineered microbes now make many longer peptides and proteins, where building them by chemistry would be too slow or wasteful.[5](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-goeddel-1979)[6](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-muttenthaler-2021) - 03 ### Build it by chemistry Solid-phase peptide synthesis builds the chain one amino acid at a time on resin beads. It suits short and medium-length peptides, which covers nearly every peptide people ask about, from BPC-157 at 15 amino acids to the 36-amino-acid HIV drug enfuvirtide, made this way at commercial scale.[3](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-behrendt-2016)[4](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-bray-2003) ## Solid-phase peptide synthesis, step by step Picture a reaction vessel half full of resin beads, each smaller than a grain of fine sand and swollen with solvent like a sponge. Each bead carries chemical handles, and the first amino acid of the peptide, the one at the end of the chain, is attached to those handles. From there the chain grows backward, from its tail toward its head. Amino acids are reactive at both ends, so each one arrives wearing a chemical cap on its front end. The most common cap today is called Fmoc. Amino acids with reactive side chains wear extra, sturdier caps on those side chains too, so nothing reacts where it should not. Then the cycle begins. First, a mild base strips the Fmoc cap from the last amino acid on the bead, exposing a free end. The beads are washed. Next, the following amino acid is added in excess, activated so it latches onto that free end. The beads are washed again, and whatever did not react drains away with the solvent. That is one cycle. A 15-amino-acid peptide needs 14 of them, and a machine can run them through the night. When the chain is complete, the beads are bathed in strong acid. The acid cuts the peptide free and removes the side-chain caps in the same step. The crude peptide is precipitated, then purified by high-performance liquid chromatography, a column that separates molecules by how strongly they cling to it. The purified fractions are pooled and freeze-dried, which is why most peptides arrive as a white, fluffy powder that is reconstituted before use.[1](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-merrifield-1986)[3](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-behrendt-2016) ## The arithmetic that decides purity Every coupling step is a chemical reaction, and no reaction is perfect. If a step works 99 percent of the time, one chain in a hundred misses that amino acid and carries on without it. Those chains are called deletion sequences, and they look almost exactly like the real thing. Multiply the small losses together and they add up. At 99 percent per step, a 15-amino-acid peptide comes off the beads with about 87 percent of chains complete. A 31-amino-acid peptide drops to about 74 percent. At 97 percent per step, the short peptide falls to around 65 percent. The rest is a crowd of near-twins, each missing one or two amino acids somewhere along the chain. Merrifield himself spent years measuring this. In a 1988 study his group used mass spectrometry to count deletion and insertion errors in model peptides, testing different recipes against each other. The best protocol reached an average stepwise yield of 99.93 percent. Modern chemistry is better again, and the Fmoc building blocks are now cheap and very pure because drug makers buy them by the ton. The practical lesson is that purity is earned at the end, in purification. A crude peptide is a family, and chromatography is what separates the intended member from its siblings. The siblings that differ by a single amino acid are the hardest to separate, and they are also the ones immunologists worry about, because a slightly wrong sequence can look foreign to the immune system.[2](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-merrifield-1988)[3](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-behrendt-2016)[10](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-degroot-2023) ## How chemists change a natural peptide Most natural peptides are fragile by design. The body makes them, uses them and clears them within minutes, so the signal stays short and precise. That is a problem when you want a medicine to last, and much of peptide chemistry is the craft of making a natural sequence sturdier without changing what it says. CJC-1295 is a good example. It starts from the first 29 amino acids of growth hormone releasing hormone. Four of them are swapped for versions that enzymes cut less easily, and a reactive group is added at the end. After injection, that group latches onto albumin, the most abundant protein in blood, and the peptide rides along with it for days. One chemical attachment turned a minutes-long signal into a weekly one. TB-500 shows the opposite move. Instead of making a long protein sturdier, it keeps only a short active stretch. Anti-doping chemists identified it as the acetylated 17 to 23 fragment of thymosin beta-4, seven amino acids taken from a protein of 43. Solid-phase synthesis makes these choices easy, since swapping in an unusual amino acid or capping an end is just another step in the cycle.[8](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-jette-2005)[9](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-esposito-2012)[6](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-muttenthaler-2021) ## What a certificate of analysis does and does not prove A peptide sold online often comes with a certificate of analysis, usually a chromatography trace and a purity number such as 98 or 99 percent. That number answers one narrow question, how much of what the detector can see is the target peptide. It does not prove the vial holds the stated amount, that it is sterile, or that something invisible to the detector is absent. Two studies show the gap. A University of Illinois group checked two custom peptides bought for research and found that one was 20 percent mannitol by weight and the other 43 percent. Mannitol, a sugar alcohol, is invisible to the usual ultraviolet detector, so the standard test had little chance of catching it. In a 2024 study of semaglutide vials bought from illegal online pharmacies, labels claimed 99 percent purity. Measured purity was 7.7 to 14.4 percent, and every vial contained bacterial endotoxin. A sound quality picture has four parts. Identity, usually by mass spectrometry, confirms the molecule is the right one. Purity, by chromatography, shows how much is the intended chain. Content tells you how much peptide is actually in the vial. And for anything injected, sterility and endotoxin testing show it will not bring bacteria or their debris with it.[11](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-choules-2020)[12](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-ashraf-2024) ## Where regulation fits in An approved peptide medicine is made to specifications reviewed by FDA. A compounded peptide is prepared by a 503A pharmacy for a named patient, from bulk ingredients, under pharmacy standards. Since October 29, 2026, FDA allows 503A compounding of six peptides, BPC-157, TB-500, epitalon, KPV, MOTS-c and Semax, under enforcement discretion while the final rule is pending. "Research use only" vials sit outside both systems, and FDA has flagged peptide-related impurities as a concern for several compounding nominations.[13](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-fda-503a)[15](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-ncpa)[14](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-fda-bulks) ## What it means for you Every peptide in every vial was assembled one link at a time, and every link carried a small chance of error. That is ordinary chemistry. What separates a clean product from a risky one is what happens afterward, how carefully the near-twins were removed and whether anyone checked the result for identity, content and sterility. So the useful questions about any peptide are who purified it and who tested it. A licensed pharmacy filling a prescription has to answer that. An anonymous seller with a purity number on a PDF does not. If you and a clinician decide a peptide makes sense, ask where it will be compounded and how that pharmacy verifies its ingredients. Then pair the course with baseline and follow-up labs, so your own blood work is the last quality check in the chain.[12](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-ashraf-2024)[13](https://www.vitalsvault.com/peptides/how-are-peptides-made#source-fda-503a) Know your baseline first 120+ lab tests at Quest, every result reviewed by a licensed clinician. Most results in 3–5 business days. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) ## Start with your labs A blood test before you start and a retest after shows what actually changed for you. It is how Vitals Vault approaches every treatment. 1. TestA baseline panel at Quest Diagnostics. 2. DecideA licensed clinician reviews your history and results. 3. RetestThe same markers again, side by side. [Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) - [Liver enzymes (ALT)Part of a metabolic panel. Checks the liver before and during any new prescription.](https://www.vitalsvault.com/biomarkers/alt) - [Kidney function (eGFR)Peptides are cleared through the kidneys, so a baseline is useful.](https://www.vitalsvault.com/biomarkers/egfr) - [hs-CRPA blood marker of inflammation you can track before and after a course.](https://www.vitalsvault.com/biomarkers/hs-crp) ![A Turkish man, 32, straight black hair in a side part, clean shaven, thick eyebrows writes in a notebook on a library step](https://www.vitalsvault.com/_next/image?url=%2Fpublic-v3%2Fshoot%2Fpeptides%2Ffaq-how-are-peptides-made.webp&w=3840&q=75&dpl=shadow-production-f0162cb4d465-40992538108-1) ## Questions How are peptides made? Most are made by solid-phase peptide synthesis, which builds the chain one amino acid at a time on resin beads, then cuts it free, purifies it by chromatography and freeze-dries it. Larger peptides such as insulin are often made by engineered microbes. A few products are extracted from animal tissue. Are peptides synthetic or natural? Many therapeutic peptides copy natural sequences exactly but are made synthetically. Others are modified copies, with swapped amino acids or added groups that make them last longer. The word synthetic describes how the chain was assembled, and says nothing on its own about safety. What is solid-phase peptide synthesis? A method invented by Bruce Merrifield in which the first amino acid is anchored to an insoluble bead and the rest are added one by one. Leftover chemicals are washed away after each step, so no purification is needed until the chain is finished. What does peptide purity mean? Purity is the share of the material, as seen by chromatography, that is the intended peptide. The rest is mostly near-copies missing an amino acid. Purity does not tell you the amount in the vial, whether it is sterile, or whether invisible fillers are present. Why are peptides sold as a powder? Peptides break down in water over time, so most are freeze-dried after purification. The dry powder is more stable for storage and shipping, and is mixed with sterile liquid before use. Is insulin a peptide? Yes. Insulin is a peptide hormone of two chains. It was first extracted from animal pancreas, and since the late 1970s it has been made by engineered microbes carrying human insulin genes. Can a certificate of analysis be trusted? It answers a narrow question. A chromatography purity figure can miss fillers the detector cannot see, and studies of online products have found purity far below the labeled number. Identity, content, sterility and endotoxin need their own tests. ## Peptides, prescribed and measured Vitals Vault is opening peptide care that starts with your blood work, is prescribed by licensed US clinicians and ends with a retest. Join the waitlist to hear first. - Prescription only - Licensed US clinicians - Quest Diagnostics labs [Get early access to peptide care](https://www.vitalsvault.com/peptides-waitlist)[Start with 120+ lab tests · $99](https://www.vitalsvault.com/labs#plans) ## Keep reading [Full Peptide Guide](https://www.vitalsvault.com/peptides) - BPC-157A 15-amino-acid peptide from a stomach protein, studied for tendon, muscle and gut repair. - TB-500A seven-amino-acid piece of thymosin beta-4, the repair protein studied for wounds, eyes and the heart. - CJC-1295A long-acting growth hormone releasing hormone analog, studied for raising growth hormone and IGF-1. - CerebrolysinA mixture of peptides and amino acids from pig brain, used in some countries for stroke and dementia, with weak evidence in Cochrane reviews. - Are peptides safe?Peptide safety comes down to the molecule, the vial it comes in and the person taking it. What the research shows about each. - FDA peptide update 2026What FDA’s October 2026 decision on six peptides means for you. ## Sources 1. 1. [Merrifield B. Solid phase synthesis. Science. 1986 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/3961484/) 2. 2. [Merrifield RB, et al. Mass spectrometric evaluation of synthetic peptides for deletions and insertions. Anal Biochem. 1988 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/3239745/) 3. 3. [Behrendt R, et al. Advances in Fmoc solid-phase peptide synthesis. J Pept Sci. 2016 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/26785684/) 4. 4. [Bray BL. Large-scale manufacture of peptide therapeutics by chemical synthesis. Nat Rev Drug Discov. 2003 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/12815383/) 5. 5. [Goeddel DV, et al. Expression in Escherichia coli of chemically synthesized genes for human insulin. Proc Natl Acad Sci U S A. 1979 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/85300/) 6. 6. [Muttenthaler M, et al. Trends in peptide drug discovery. Nat Rev Drug Discov. 2021 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/33536635/) 7. 7. [Gevaert B, et al. Peptide profiling of Internet-obtained Cerebrolysin using liquid chromatography and mass spectrometry. Drug Test Anal. 2015 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/26017115/) 8. 8. [Jetté L, et al. Human growth hormone-releasing factor (hGRF)1-29-albumin bioconjugates activate the GRF receptor on the anterior pituitary in rats: identification of CJC-1295 as a long-lasting GRF analog. Endocrinology. 2005 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/15817669/) 9. 9. [Esposito S, et al. The N-terminal acetylated 17–23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal. 2012 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/22962027/) 10. 10. [De Groot AS, et al. Immunogenicity risk assessment of synthetic peptide drugs and their impurities. Drug Discov Today. 2023 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/37467878/) 11. 11. [Choules MP, et al. NMR reveals an undeclared constituent in custom synthetic peptides. J Pharm Biomed Anal. 2020 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/31671336/) 12. 12. [Ashraf AR, et al. Multifactor quality and safety analysis of semaglutide products sold by online sellers without a prescription. J Med Internet Res. 2024 (opens in a new tab)](https://pubmed.ncbi.nlm.nih.gov/39509151/) 13. 13. [FDA. Bulk drug substances used in compounding under section 503A (opens in a new tab)](https://www.fda.gov/drugs/human-drug-compounding/bulk-drug-substances-used-compounding-under-section-503a-fdc-act) 14. 14. [FDA. Certain bulk drug substances for use in compounding that may present significant safety risks (current as of April 22, 2026) (opens in a new tab)](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) 15. 15. [NCPA. FDA grants enforcement discretion for compounding six peptides. October 29, 2026 (opens in a new tab)](https://ncpa.org/newsroom/qam/2026/10/29/fda-grants-enforcement-discretion-compounding-six-peptides) Written by the Vitals Vault editorial team, medically reviewed by Robert Lufkin, MD, and updated October 29, 2026. This is general education, not medical advice. None of these peptides is FDA-approved to diagnose, treat, cure or prevent any disease, and compounded medicines are not FDA-reviewed for safety, effectiveness or quality. 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