For several decades, exogenous steroid hormones have been explored by researchers and pet owners alike to contracept dogs and cats. Administered in either injectable or oral forms, they cause hormonal down-regulation and can suppress fertility with consistent use. They can work via a variety of mechanisms, including suppression of GnRH through negative feedback at the level of the brain or pituitary gland, or by direct effects on the uterus (females) or sperm transport (males). The regularity with which animals must be treated is one limitation of hormonal treatments; adverse side effects are another reason why ACC&D generally discourages these options, particularly for long-term use.

Progestins are a class of synthetic compounds that are structurally similar to progesterone and mimic its biological effect. Low-dose megestrol acetate (MA), available through veterinary compounding agencies, and available in the E.U. under multiple product names, is one example. ACC&D has encouraged consideration of MA as a stopgap tool to manage delays in access to spay surgery to prevent conception in female cats. See more on our MA page. Some pet owners and veterinary practitioners also seek medroxyprogesterone acetate (brand names include Provera® and Depo-Provera®) to suppress heat cycles in female dogs, oftentimes with extremely serious adverse health consequences. More information is available here.

Androgen steroids control and stimulate male sex characteristics and have been used to suppress fertility in female dogs. Mibolerone (formerly sold as Cheque® Drops) is a synthetic androgen historically used to prevent estrus in dogs. Mibolerone works via negative feedback to block the release of luteinizing hormone (LH) required for pregnancy. Potential adverse side effects should be carefully considered before using androgen steroids for fertility control.