What are peptides? Meaning, medicines, safety and legal status in Australia

What are peptides?

A peptide is a short chain of amino acids, the small units from which proteins are made (TGA peptide products page, 23 September 2026). Neighbouring amino acids are joined by peptide bonds, and databases of peptide structures count a chain as a peptide when it has fewer than 50 amino acids (Hamdani et al., Protein Science, 2026). The word peptide therefore describes a structure, not a purpose. Insulin, a collagen supplement, a cosmetic serum and an unapproved product sold online can all be called peptides, yet each has a different regulatory status in Australia (TGA, 23 September 2026).

Your body makes peptides all the time. Pancreatic beta cells release insulin, a peptide hormone, into the blood (Leighton et al., Diabetes Therapy, 2017). The TGA says natural peptides are involved in the signalling that governs growth, metabolism and tissue repair (TGA, 23 September 2026). Peptides made as medicines usually have a molecular weight of 500 to 5,000 daltons, which sits between small-molecule drugs and large proteins (Wang et al., Signal Transduction and Targeted Therapy, 2022). How peptides are built, bond by bond, has its own page.

For readers in Australia the question has a legal edge. The TGA says a peptide product is regulated as a therapeutic good if it is promoted, supplied or generally used for a therapeutic purpose, and that products with claims limited to cosmetic purposes may be regulated as cosmetics instead (TGA, 23 September 2026). The Australian law hub sets out the schedule status of named compounds. This page covers the general questions.

What are the main types of peptides?

The sources checked for this page on 14 October 2026 use several classification schemes rather than one four-type list. Three schemes appear in the sources checked: by length, by origin and by job. By length, the National Library of Medicine's MeSH vocabulary treats chains of fewer than 13 amino acids as oligopeptides (MeSH record for Peptides, checked 14 October 2026). By origin, peptides come from the ribosome, from non-ribosomal enzymes in bacteria and fungi, or from chemical synthesis (Wang et al., 2022). By job, they include hormones, host-defence peptides and cell-penetrating peptides.

Hormone peptides are the best known. Insulin, oxytocin, vasopressin and gonadotropin-releasing hormone (GnRH) are natural hormones whose study started the field of therapeutic peptides (Wang et al., 2022). Host-defence peptides, also called antimicrobial peptides, are made by many organisms and can kill microbes directly or shape the immune response (Mookherjee et al., Nature Reviews Drug Discovery, 2020).

Non-ribosomal peptides, such as vancomycin and cyclosporin, come mainly from bacteria and fungi (Wang et al., 2022). The sorting schemes overlap. A single molecule can be short, made by a cell and a hormone all at once. Cell-penetrating peptides, a group defined by one property, are covered in the FAQ below.

Are peptides steroids?

No. Peptides and steroids are different chemical families. A peptide is a chain of amino acids. A steroid hormone is built from cholesterol, which cells convert into steroid hormones through a series of enzyme steps (Miller and Auchus, Endocrine Reviews, 2011). Testosterone, for example, has the formula C19H28O2 and no amino-acid chain (PubChem record for testosterone, checked 14 October 2026). The confusion comes from sport and regulation, where both families sit on the same lists: the World Anti-Doping Agency (WADA) 2026 Prohibited List puts anabolic agents, including steroids, in class S1 and peptide hormones, growth factors and mimetics in class S2, and bans both at all times (WADA 2026 Prohibited List).

A steroid peptide is therefore not a standard category. People who search for it often mean a peptide that acts on the body's own steroid production. WADA lists such peptides in class S2.2.1 as testosterone-stimulating peptides in males, naming chorionic gonadotrophin, luteinizing hormone, GnRH and kisspeptin (WADA 2026 Prohibited List, in force from 1 January 2026).

The phrase the new steroids is a comparison made in talk and media, not a classification in the sources checked. What the TGA does say, in its 20 July 2026 media release, is that peptide products continue to be promoted online for weight loss, anti-ageing, muscle growth, performance enhancement and cosmetic purposes.

Are peptides drugs, and which medicines are peptides?

Some peptides are medicines and many are not. The TGA lists insulin and insulin analogues, glucagon-like peptide-1 (GLP-1) receptor agonists such as semaglutide, oxytocin, desmopressin and octreotide as approved peptide-based medicines (TGA guidance on peptide regulation, checked 14 October 2026). More than 80 peptide drugs have been approved worldwide (Wang et al., 2022; Muttenthaler et al., Nature Reviews Drug Discovery, 2021). Natural peptides in the body, peptides in food and cosmetic peptides are not medicines by default. Regulation depends on the contents, promotion and intended purpose of each product (TGA, 23 September 2026).

The table below lists selected peptide drugs approved since 2000, with the uses their approvals name, taken from Table 1 of Wang et al. (2022). Type 2 diabetes is the largest group in that table, with six GLP-1 receptor agonists approved between 2005 and 2017. The range is wide: osteoporosis, cancer, bowel conditions, pain and rare diseases all appear. The uses are regulators' approved indications, quoted for information.

By sales, the top-selling non-insulin peptide drugs in 2019 were three GLP-1 medicines: dulaglutide (Trulicity) at $4.39 billion, liraglutide (Victoza) at $3.29 billion and semaglutide (Rybelsus) at $1.68 billion in retail sales, within worldwide peptide drug sales above $70 billion (Wang et al., 2022, citing Njardarson's analysis). Those are 2019 figures, and this page reports no newer ones. The guide to the SURPASS and SURMOUNT trials shows how the trial record behind two of these medicines is read.

Is there a top, number one or most popular peptide?

No regulator or journal source checked for this page on 14 October 2026 supplied a single ranking of peptides as a group, and the question has no single answer. Rankings that can be checked use a stated measure. By 2019 retail sales, the top three non-insulin peptide drugs were GLP-1 medicines (Wang et al., 2022). By approvals, the field counts more than 80 peptide drugs and no single winner (Muttenthaler et al., 2021). By trial results, comparisons hold only inside one trial, such as the 72-week SURMOUNT-5 trial that compared tirzepatide with semaglutide in 751 adults, an open-label trial funded by the maker of tirzepatide that applies to those two medicines only (Aronne et al., New England Journal of Medicine, 2025).

Terms such as king and number one are marketing words. A fair ranking needs a stated goal, a stated measure and a head-to-head comparison, and the head-to-head trials in the sources checked for this page concern approved medicines. None of the sources checked ranks the unapproved peptides promoted online, and the TGA states that it has reviewed no scientific evidence for their safety or for the claims made for them (TGA safety advisory, 13 April 2026).

Questions that ask which three peptides a person should pick also ask for a personal choice, which no source on this page can make. The pages in the peptide science hub report what studies of single compounds found, with the model, the size and the limits.

Evidence limits

What problems have been recorded with unapproved peptide products?

A case the TGA published on 14 September 2026 shows why contents matter. A consumer who reported using a product sold as retatrutide had uncontrollable vomiting, a torn oesophagus and hospital treatment, and TGA laboratory testing of a single sample of the product, held in its original unmarked vial, found undeclared semaglutide and no retatrutide, at approximately 8 times the semaglutide level found in semaglutide products on the Australian Register of Therapeutic Goods; one report does not give a rate, and the finding describes that sample (TGA safety advisory, 14 September 2026).

The TGA's page on buying peptide products online says unapproved products may fall short of quality or safety standards, may contain the wrong active ingredient or far more or less than the label states, may not be sterile, and may cause serious adverse events, including severe allergic reactions, infection and liver damage (TGA, risks of buying peptide products online, checked 14 October 2026). For BPC-157, a systematic review of 36 studies found 35 preclinical studies and one clinical study, and reported that it located no clinical safety data within its search (Vasireddi et al., HSS Journal, 2025).

Which people do medicine labels exclude, and what do they say about liver and kidneys?

Prescribing information for approved peptide medicines lists exclusions and warnings drawn from trials. The US label for Ozempic (semaglutide, a GLP-1 medicine; revised June 2026) lists two contraindications: a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2, and a serious hypersensitivity reaction to semaglutide (DailyMed Ozempic label, checked 14 October 2026). The same label lists acute pancreatitis, gallbladder disease and acute kidney injury due to volume depletion among its warnings (DailyMed Ozempic label, checked 14 October 2026).

Those lists belong to one medicine. They do not carry over to other peptides, and an unapproved product has no label of this kind. The TGA says that when a health practitioner accesses an unapproved peptide product for a patient, responsibility for judging its quality and safety rests with the practitioner, because the TGA has not assessed it (TGA, information for health practitioners, checked 14 October 2026).

The label for another approved peptide, bremelanotide (Vyleesi), lists a different contraindication: uncontrolled hypertension or known cardiovascular disease (DailyMed Vyleesi label, checked 14 October 2026). The difference shows that each label reflects its own trials and that no single list of exclusions covers all peptides.

On liver and kidneys, the TGA lists liver damage among the serious adverse events that unapproved peptide products may cause (TGA risks page, checked 14 October 2026). The 2025 systematic review of 36 BPC-157 studies reported that it located no clinical safety data within its search (Vasireddi et al., 2025). No controlled human study of liver or kidney effects of the research peptides promoted online was found in the sources checked.

Is there much science behind peptides, and are peptides worth it?

Peptide science is large for approved medicines and thin for most products sold as research compounds. Since insulin entered medicine almost a century ago, more than 80 peptide drugs have reached the market for diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain (Muttenthaler et al., 2021). More than 170 peptides are in active clinical development (Wang et al., 2022). For BPC-157, a peptide often discussed online, a 2025 systematic review found 36 studies, of which 35 were preclinical and one was a clinical report (Vasireddi et al., 2025).

Worth it is a value judgement, and studies measure outcomes in defined groups, not worth. Regulators ask a narrower question: do the quality, safety and effectiveness data support approval for a named use? The TGA states that approved peptide-based medicines are tested broadly in human clinical trials before approval (TGA regulatory guidance on peptide products). Unapproved products have not had that assessment.

Evidence ranges from cell studies to large trials. In the 72-week SURMOUNT-1 trial of 2,539 adults without diabetes, mean weight change at week 72 was 15.0%, 19.5% and 20.9% across the three tirzepatide groups, against 3.1% with placebo, in a trial of an approved medicine funded by its developer that says nothing about research material (Jastreboff et al., New England Journal of Medicine, 2022).

Why are so many people talking about peptides, and what about celebrity claims?

The TGA reports a significant increase in the online promotion, advertising and supply of peptide products, which it says are promoted for weight loss, muscle growth, anti-ageing, recovery and performance enhancement (TGA media release, 20 July 2026; TGA peptide products page, 23 September 2026). No regulator or journal source checked measures how many people use peptides, so this page gives no figure. Claims about named public figures are interview or social-media statements, not clinical records, and this page reports none of them.

Attention and evidence are different things. The TGA says unapproved peptide products are being advertised as delivering fast health results while they can pose serious health risks (TGA media release, 20 July 2026), and that influencers and online sellers who promote unapproved peptide products may be held accountable for unlawful advertising (TGA, 20 July 2026). A name attached to a product is a promotion, not a study.

Questions about what a particular celebrity or podcaster takes have no sourced answer either. No peer-reviewed paper or regulator page located for this page documents what any named person takes, so the record in the sources checked is empty.

What is C-peptide, and why is it measured instead of insulin?

C-peptide is a 31-amino-acid peptide cut from proinsulin, the precursor molecule, and released from pancreatic beta cells in equal amounts with insulin (Leighton et al., Diabetes Therapy, 2017). Laboratories measure C-peptide instead of insulin because it stays in the blood longer. C-peptide has a half-life of 20 to 30 minutes against 3 to 5 minutes for insulin, and the liver removes about half of the insulin secreted but almost none of the C-peptide, which gives a steadier reading of the body's own insulin output (Leighton et al., 2017). C-peptide is also called the proinsulin connecting peptide (Shao et al., International Journal of Molecular Sciences, 2026).

Insulin made by the body and insulin made as a medicine look alike to an insulin test, but C-peptide separates them. C-peptide does not come from insulin made as a medicine, so a C-peptide result reflects the person's own pancreas, even in someone treated with insulin (Leighton et al., 2017). The biological role of C-peptide itself remains poorly understood (Shao et al., 2026).

The role of C-peptide in insulin production is mostly one of origin: cleavage of proinsulin yields insulin and C-peptide in equal amounts (Leighton et al., 2017). That equal split is why a C-peptide measurement works as a proxy for insulin secretion.

What is a good C-peptide level, and what do high or low levels mean?

No single good C-peptide level exists, because laboratories use different assays and units and ranges depend on the population tested (Jones and Hattersley, Diabetic Medicine, 2013). In healthy people, fasting plasma C-peptide is reported as 0.3 to 0.6 nmol/L, rising to 1 to 3 nmol/L after a meal, and ranges vary with the assay and the population tested (Leighton et al., 2017). A level below 0.2 nmol/L is associated with a diagnosis of type 1 diabetes in that review, and clinicians read results in context, not alone (Leighton et al., 2017). A high level means the pancreas is releasing a lot of insulin, which can occur with insulin resistance, and the meaning of a given level depends on the person (Jones and Hattersley, 2013).

Reading a C-peptide result is a clinical task. Blood C-peptide can read falsely high in kidney impairment, because about half of C-peptide is removed by the kidneys, and the meaning of a given level depends on a person's insulin resistance (Jones and Hattersley, 2013). An obese, insulin-resistant person may have normal or high C-peptide even with autoimmune type 1 diabetes (Jones and Hattersley, 2013). High values therefore do not point to one cause. C-peptide testing also helps assess conditions such as insulinoma, a tumour that secretes insulin (Leighton et al., 2017).

The sources use three units: 1 nmol/L equals 1,000 pmol/L and 3 ng/mL (Jones and Hattersley, 2013). A value is meaningless without its unit and the laboratory's own range.

Which foods contain peptides?

Every food that contains protein contains amino acids linked by peptide bonds, and digestion breaks food proteins into peptides and amino acids. Food proteins also carry hidden peptide sequences that can act as signals once released, so reviews call them food-derived bioactive peptides (Chakrabarti et al., Nutrients, 2018; Daliri et al., Foods, 2017). No ranking of foods by total peptide content was found in the sources checked. The one direct food measurement located covers glutathione, a tripeptide: in a 1992 survey it was moderate to high in fruits and vegetables, relatively high in freshly prepared meats and low in dairy products, cereals and breads, a measure of one compound that does not rank foods by total peptide content (Jones et al., Nutrition and Cancer, 1992).

Absorption decides which peptides reach the blood. The intestine takes up di- and tripeptides through a transporter called PEPT1, and neither free amino acids nor peptides of four or more amino acids are accepted by that transporter (Daniel, Annual Review of Physiology, 2004). Longer peptides are broken down first. The food-peptide reviews add that well-designed clinical trials of food-derived peptides remain scarce (Daliri et al., 2017; Chakrabarti et al., 2018).

In a 1992 survey measuring glutathione in foods, processing and preservation other than freezing generally reduced measured glutathione; this finding concerns that tripeptide and does not measure total food-peptide content (Jones et al., 1992).

What has been recorded about the safety of collagen peptides?

The sources checked for this page record one allergy finding for fish-derived collagen and a call for more long-term safety research, not a measured rate of adverse events. In a 2000 study of 10 children with fish allergy, 3 had IgE antibodies, the immune proteins behind allergic reactions, to fish gelatin, which is type I collagen, so fish collagen might be an allergen in people with fish allergy, and the small study did not test collagen supplements (Sakaguchi et al., Journal of Allergy and Clinical Immunology, 2000). A 2025 narrative review of hydrolysed marine collagen states that long-term safety should be a primary concern of future research (Bartoletti et al., Clinical, Cosmetic and Investigational Dermatology, 2025).

The 2021 meta-analysis of 19 randomised, double-blind, controlled trials with 1,125 participants focused on skin outcomes, not safety (de Miranda et al., International Journal of Dermatology, 2021), so it cannot settle safety questions. The 2025 marine collagen review is a narrative review, which summarises other studies and ran no trial of its own (Bartoletti et al., 2025).

In a 2000 laboratory analysis of serum samples from three small patient groups (10, 2 and 15 patients), IgE antibodies showed little cross-reactivity between fish and bovine gelatins, and the study did not test hydrolysed collagen supplements (Sakaguchi et al., Journal of Allergy and Clinical Immunology, 2000). The peptide comparison guide sets marine and bovine collagen side by side.

Are research peptides legitimate, and how can anyone check a peptide seller?

Legitimate has two separate meanings: lawful and verifiable. On lawfulness, the TGA states that a research use only or not for human use disclaimer does not change whether a product is regulated as a therapeutic good (TGA, how peptide products are regulated). On verifiability, a seller cannot be judged from its own website alone, because the TGA warns that unapproved products may be wrongly labelled or contain far more or less active ingredient than the label states (TGA, risks of buying peptide products online). Records bear on both meanings, and the supplier checklist lists ten of them.

A certificate of analysis (COA) is a test report for a named batch, and it documents only the lot, the compound and the test method it names. A report for a different lot says nothing about another batch.

This page does not rank or review named sellers. Reviews, most trusted lists and company comparisons rest on opinion, and none of the regulator or journal sources checked evaluates individual suppliers. The TGA says it works with the Australian Border Force to stop unlawful imports of unapproved peptide products (TGA, 23 September 2026).

Can peptides be brought into Australia, seized at the border or sold here?

Importing and supplying a peptide product in Australia depends on its status on the Australian Register of Therapeutic Goods (ARTG). Unapproved peptide products cannot be imported or supplied unless a valid exemption, approval or authority applies. The Personal Importation Scheme covers an import only if every condition is met, including personal or immediate-family use and, for prescription-only medicines, a valid Australian prescription (TGA guidance on peptide regulation; TGA Personal Importation Scheme page, updated 8 September 2026). Goods that do not meet the conditions may be seized and destroyed, and the buyer can lose both the goods and the money paid.

The TGA's 7 May 2026 advisory says the peptide imports it sees are often poorly labelled, that vials it cannot identify are not released under the scheme, and that it will notify the Australian Border Force to seize them (TGA safety advisory, 7 May 2026). The scheme's 8 September 2026 changes clarify the evidence needed by people travelling to Australia with prescription-only medicines (TGA, 8 September 2026). The sources checked cover import into Australia and do not address airline rules for domestic flights.

Selling is a separate question. The TGA says it is generally unlawful to advertise unapproved therapeutic goods to the Australian public, and that supply of unapproved goods is prohibited unless an exemption applies. Penalties under the Act include civil penalties of up to $1.82 million per breach for individuals and $18.2 million per breach for corporations, and criminal penalties of up to 7 years imprisonment (TGA safety advisory, 14 September 2026). Anyone can report suspected unlawful supply or advertising to the TGA through its report a perceived breach form. The law hub covers schedule status by compound.