Thymosin Alpha-1 is a 28 amino acid peptide first found in the thymus, the gland that trains the immune system's T cells. Its synthetic form, thymalfasin (brand name Zadaxin), is approved as a medicine in more than 30 countries, mainly for chronic hepatitis B and as immune support. It helps regulate immune responses rather than simply boosting them. It is one of the better studied peptides, but it is still a prescription treatment that a physician should choose and monitor.

Epithalon (also spelled Epitalon) is a small synthetic peptide of four amino acids, developed in Russia from a pineal gland extract. Lab studies show it can switch on telomerase, the enzyme that protects the ends of chromosomes, and small human studies suggest it may help restore melatonin rhythm in older adults. Most of the research comes from one group, and there is no proof that it extends human life. It is best seen as an experimental longevity option, used with a physician and alongside proven habits.