Are peptides steroids?

No. Peptides and steroids are different classes of molecule, and SARMs, which often come up in the same conversation, are a third. They differ in what they are built from, how they are made, how they work at a molecular level and how UK law treats them. This guide sets out those differences.

Research use only, and not medical or legal advice. This guide compares three classes of molecule as chemistry. It says nothing about using any of them in people or animals, and nothing here is dosing, medical or legal advice.

The short answer

• Peptides are chains of amino acids joined by peptide bonds.
• Steroids are lipids built on a skeleton of four fused carbon rings.
• SARMs (selective androgen receptor modulators) are small synthetic molecules, most of them non-steroidal, designed to bind the androgen receptor.

A peptide has no steroid ring system, so no peptide is a steroid. The mix-up usually comes from two things the groups share: both include natural hormones, and both appear on anti-doping lists.

What makes a peptide a peptide

A peptide is built from amino acids, the same building blocks as proteins. Each amino acid is joined to the next by a peptide bond, an amide link between the carboxyl group of one and the amino group of the next. A peptide is therefore a specific sequence of amino acids. By convention, chains of up to about 50 amino acids are called peptides and longer ones proteins, although the cut-off is not strict.

Size varies a lot. GHK, the peptide in GHK-Cu, is three amino acids long. BPC-157 is 15, with a molecular weight of about 1,420 daltons. Tesamorelin is 44. Most peptides are water-soluble, and in the laboratory they are usually made by solid-phase peptide synthesis, which builds the chain one amino acid at a time on a resin support.

What makes a steroid a steroid

A steroid is defined by its shape, not its job. IUPAC defines steroids as compounds with the cyclopenta[a]phenanthrene skeleton, or a skeleton derived from it: three six-membered carbon rings and one five-membered ring, fused together. In animals, steroid hormones are made from cholesterol, which is itself a steroid. Industrially, most steroid drugs are made by semi-synthesis from plant sterols.

Steroids are small and lipid-soluble. Testosterone has a molecular weight of about 288 daltons, roughly a fifth of BPC-157's. Familiar examples include cholesterol, cortisol, oestradiol and testosterone. Anabolic-androgenic steroids are synthetic compounds derived from or modelled on testosterone, and they are what most people mean by "steroids".

Where SARMs fit

SARMs are not peptides, and most of them are not steroids either. They are small synthetic molecules, typically 300 to 450 daltons, made by multi-step organic synthesis and designed to bind the androgen receptor, the receptor testosterone binds. The anti-doping list names examples such as enobosarm (ostarine), LGD-4033 and RAD140. One listed compound, YK-11, does have a steroid skeleton, which is why "most" matters. SARMs were developed as drug candidates, and none is a licensed medicine in the UK.

Side by side

"Hormone" describes a job, not a structure

Part of the confusion is that the word hormone cuts across both groups. A hormone is a signalling molecule carried in the blood, and nature uses both chemistries for the job. Insulin, oxytocin and growth hormone are peptide or protein hormones. Testosterone, oestradiol and cortisol are steroid hormones. Calling a molecule a hormone tells you what it does in the body, not what it is made of, so a peptide hormone and a steroid hormone are two different kinds of molecule.

The difference shows in how they work. Peptide hormones are mostly water-soluble and act through receptors on the cell surface. Steroid hormones are lipid-soluble, pass through the cell membrane and act mainly through receptors inside the cell.

How UK law treats each

Anabolic steroids are Class C controlled drugs. Schedule 2 of the Misuse of Drugs Act 1971 names testosterone and dozens of related compounds, with a catch-all for compounds structurally derived from them. Supplying them is a criminal offence.

A few peptide hormones are on the same list. The same part of the Act names human chorionic gonadotrophin (hCG), non-human chorionic gonadotrophin, and somatotropin, somatrem and somatropin, which are forms of growth hormone.

Most research peptides are not controlled drugs. Peptides such as BPC-157 and TB-500 are not scheduled under the Act. They are not licensed medicines either: under the Human Medicines Regulations 2012, supplying a product for human use without a marketing authorisation is unlawful, which is why research peptides are sold for in-vitro laboratory research only. Our guide to whether peptides are legal in the UK covers this in more detail.

SARMs are not licensed medicines in the UK.

This is general information about how the law classifies these substances, not legal advice. The controlled-drugs lists change, so check the current text for any specific compound.

In sport, all three are banned

The World Anti-Doping Agency's Prohibited List, which UK Anti-Doping applies in the UK, bans all three groups at all times, in and out of competition:

• S1.1 covers anabolic androgenic steroids.
• S1.2 covers other anabolic agents and names SARMs, including enobosarm (ostarine), LGD-4033 and RAD140.
• S2 covers peptide hormones, growth factors, related substances and mimetics, including thymosin-β4 derivatives such as TB-500.
• S0 covers non-approved substances and names BPC-157.

For anti-doping purposes, then, whether a substance is a peptide or a steroid makes no practical difference.

Where research peptides fit

Research peptides are peptides: amino-acid chains with no steroid ring system. MY PEPTIDES supplies them strictly for in-vitro laboratory research, with a batch Certificate of Analysis for each product, and does not advise on human or animal use. For background on the category, see what are research peptides?