Cypionate

Cypionate is the ester of cyclopentylpropionic acid used in pharmacology. In drug design, cypionate refers to the cyclopentylpropionate ester formed with an active molecule, most notably testosterone to give testosterone cypionate. The ester increases lipophilicity and slows release after intramuscular injection, extending the drug's duration of action compared with the non-esterified form.

The most widely used example is testosterone cypionate, a long-acting androgen employed in testosterone replacement therapy for adult males with hypogonadism. It is also used in gender-affirming hormone therapy for transgender men. Dosing is generally every 2 to 4 weeks, adjusted to clinical response and testosterone levels.

Administration is by intramuscular injection in an oil-based vehicle such as sesame or cottonseed oil. After injection, hydrolysis of the ester releases active testosterone; peak concentrations occur within several days and the apparent half-life is on the order of 7–9 days, though the therapeutic effect lasts longer in vivo.

Safety considerations include typical androgenic effects (acne, hair growth, mood changes), polycythemia, edema, and potential cardiovascular risks. It is contraindicated in pregnancy, lactation, and in certain prostate conditions. Monitoring typically includes hematocrit, lipid profile, liver function, and assessment for signs of androgen excess.

In addition to testosterone, the term cypionate can describe other drug esters formed with cyclopentylpropionic acid, used to prolong the activity of diverse compounds, though testosterone cypionate is the most prominent example.