Altrenogest, sold under the brand names Swinemate and Altren manufactured by Aurora Pharmaceutical and Regumate manufactured by Merck, is a progestin of the 19-nortestosterone group which is widely used in veterinary medicine to suppress or synchronize estrus in horses and pigs.

An in vitro yeast structure–activity relationships bioassay study found that altrenogest was the most potent agonist of both the progesterone receptor (PR) and the androgen receptor (AR) of a large selection of other progestogens as well as anabolic–androgenic steroids (AAS).

[9] The observed potency of altrenogest even exceeded that of metribolone (methyltrienolone, R-1881), which was the second most potent compound.

[9] According to its manufacturer Roussel Uclaf, altrenogest has weak anabolic and androgenic activity equivalent to 1/20th of that of testosterone.

[10] However, no significant androgenic effects have been observed in young stallions or mature mares,[11] and altrenogest has notably been used to maintain pregnancy in mares (similarly to the use of allylestrenol to maintain pregnancy in women) with no incidence of virilization or other abnormalities in filly offspring.