Peptide may not yet be the 2026 Oxford Word of the Year, but it must surely be in the running.

From your friendly neighbourhood influencer, to the gym bros, injectable peptides have been all over social media and are now making mainstream news when things go horribly wrong.

People are taking them, and promoting them, for a seemingly endless list of reasons. Depending on who you ask, they’ll either put a pep in your step, give you a tan, make your skin glow, or even build you bigger muscles.

But for those of us not immersed in this new form of chemical pop culture, what the heck are they?

Read more: Influencers are promoting dangerous peptides on social media – and regulators are struggling to keep up

They’re chemical messengers

Many peptides occur naturally in the body (endogenous), or in the food we eat (exogenous). These short chains of amino acids are smaller than proteins and are entirely natural.

However, the peptides created in labs for varied purposes are synthetic.

Within the body, peptides act as precision chemical messengers regulating critical processes such as metabolism, growth, immunity, and tissue repair and building.

They are water-soluble, so they cannot pass directly through cell membranes. Instead, they bind to receptors on the surface of target cells to trigger a cascade of events inside the cell.

Some key categories of peptides include:

peptide hormones (such as human growth hormone). These regulate metabolism, growth and other whole-body processes

peptide hormones (such as human growth hormone). These regulate metabolism, growth and other whole-body processes

neuropeptides (endorphins). These signal within the brain and nervous system to influence things such as mood, appetite and pain

neuropeptides (endorphins). These signal within the brain and nervous system to influence things such as mood, appetite and pain

growth factors........

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