 At high doses, the duration of action of gestonorone caproate by intramuscular injection has been found to be at least 21 days.Clinical studies have found gestonorone caproate to be satisfactorily effective as a progestogen when injected once a month, whereas it was poorly effective as an injectable contraceptive when it was injected once every two months.Following a single intramuscular injection of 200 mg radiolabeled gestonorone caproate in 1 mL of solution in men with prostate cancer, maximal levels of gestonorone caproate occurred after 3 ± 1 days and were 420 ± 160 ng/mL.