A comparison of the potencies and activities of progestogens used in contraceptives.

The potencies and activities of six progestational agents, norethindrone, levonorgestrel, desogestrel, medroxyprogesterone acetate (MPA), progesterone (P) and norgestimate have been evaluated using standard laboratory bioassays. The endocrine activities measured are those most closely related to the clinically important actions of contraceptives. Relative potencies varied with parameter measured, route of administration and species showing clearly that each progestogen is a distinct pharmacological entity. The order of potency using oral administration for either ovulation inhibition or endometrial stimulation in rabbits was desogestrel greater than levonorgestrel greater than MPA greater than norgestimate greater than norethindrone. Levonorgestrel was more androgenic than desogestrel, and P, norethindrone, norgestimate and MPA were essentially devoid of androgen activity. This profile demonstrates clear differences in the potencies and activities of these progestogens and in their selectivity for target organs.