Peptides you already know without realizing it

In step 1 we saw that a peptide is a short chain of amino acids (the small pieces the body uses to build its proteins). If amino acids are letters, peptides are short words and proteins are whole books. Today we take the second step, and it is a reassuring one: you already know several peptides. You have probably prescribed them, seen them on the hospital ward or have them in your own bathroom cabinet.

The most famous one: insulin

Insulin is the hormone that helps sugar move from the blood into cells. It is a small molecule, made of two short chains of amino acids joined together¹⁵. Its arrival in medicine, just over a century ago, changed the lives of people with diabetes¹⁴.

Insulin also opened a door. A review in Nature Reviews Drug Discovery puts it this way: «Since the introduction of insulin almost a century ago, more than 80 peptide drugs have reached the market»¹. Diabetes, cancer, osteoporosis, multiple sclerosis, HIV infection and chronic pain are among the areas where they are used today¹.

Oxytocin: nine amino acids with a history

Oxytocin is another peptide almost every physician knows, for its role in reproduction: among other things, it stimulates uterine contractions during labor and milk ejection during breastfeeding⁷. It is tiny: just nine amino acids. Its story is a landmark in chemistry. Vincent du Vigneaud worked out its composition in 1953; it became the first peptide hormone to have its sequence (the exact order of its amino acids) determined, and he also managed to make it in the laboratory².

That work earned him the 1955 Nobel Prize in Chemistry². Making a peptide identical to the natural one seemed out of reach at the time. Today it is routine in laboratories around the world, and that ability underpins everything we will cover in this series.

Semaglutide and tirzepatide: the peptides of the moment

If you have heard of Ozempic, Wegovy or Mounjaro, you have heard of peptides. Semaglutide mimics GLP-1, a hormone the gut releases after a meal that, among other things, tells the brain that food is on its way⁹. Chemists designed it with only a few changes from human GLP-1 and a fatty-acid chain that makes it last much longer in the blood⁸. Tirzepatide goes one step further: it mimics two gut hormones at once, GLP-1 and GIP¹⁰.

The results have been remarkable. In the STEP 1 trial, with 1,961 adults with overweight or obesity, the semaglutide group lost an average of 14.9% of body weight over 68 weeks, compared with 2.4% on placebo (an inactive substance used for comparison)³. Few recent medical stories have made such a splash, and at the center of all of them sits a peptide. With tirzepatide, in the SURMOUNT-1 trial, average weight loss at 72 weeks reached 20.9% in the highest-dose group, versus 3.1% on placebo¹⁶.

Octreotide: a hospital peptide

Octreotide is a laboratory version of somatostatin, a natural hormone that acts as a brake on other hormones. The natural version lasts only a very short time in the blood; octreotide was designed to last much longer. It is a good example of how chemists tune a natural peptide to make it more practical¹¹.

It has been used for years in neuroendocrine tumors (tumors that arise from hormone-producing cells). In the PROMID study, the time until the tumor progressed was 14.3 months with octreotide versus 6 months with placebo⁴. A peptide of just eight amino acids, at work in oncology.

Peptides in the kitchen and on the vanity

Not every peptide is a medicine. Hydrolyzed collagen (collagen cut into small pieces so it is easy to digest) is sold as powders, gummies and drinks. Many of those pieces are peptides. A meta-analysis (a study that pools the results of many trials) combined 19 trials with 1,125 participants and found better skin hydration, elasticity and fewer wrinkles versus placebo⁵. Another meta-analysis, of 26 trials with 1,721 participants, also found better hydration and elasticity, although its authors call for larger trials to confirm it¹².

In cosmetics, the best-known example is Matrixyl, the trade name for palmitoyl pentapeptide-4: five amino acids attached to a fatty acid that helps the molecule get along with the skin. It was designed to stimulate collagen, inspired by a five-amino-acid fragment of type I procollagen that stimulated collagen production in fibroblasts¹³. In a 12-week trial in 93 women, the cream with this peptide reduced wrinkles and fine lines compared with the same cream without it⁶.

The idea to take home

Insulin, oxytocin, semaglutide, tirzepatide, octreotide, collagen, Matrixyl. Different molecules with different uses, yet all of them are short chains of amino acids. Peptides are neither strange nor new: they are one of the most studied families of molecules in medicine.

When later steps cover research peptides such as GHK-Cu or BPC-157, think back to this list. They are cousins of molecules you already know. The message they carry changes, but the alphabet is the same.