the real name is Mibolerone. Mibolerone is used to prevent dogs from coming into heat, and in the treatment of some causes of infertility. I do not use them for this.. but... here is a little inside info on this stuff.....
FDA approved for use in dogs for estrus suppression. Mibolerone is an androgenic steroid which opposes the effects of estrogen and other hormones which cause ovulation and subsequent production of progesterone. Need to start the medication at least 30 days before proestrus to prevent the female from coming into heat. It is about 90% effective. Do not use in dogs which are to be bred in the future as start of the next cycle may vary from 7-200 days from discontinuation of Cheque Drops. It has been used to lengthen short cycles which cause infertility and to treat false pregnancies. The false pregnancy may recur when the medication is discontinued. Because of this and the fact that most false pregnancies resolve on their own, no treatment is usually given. The most effective way to prevent these problems in dogs who are not showing in the breed ring and are not going to be used for breeding is by an ovariohysterectomy (spay).
Cheque drops (Upjohn) will shut down the cycling of the ovary. This removes the progesterone influence which is responsible for promoting uterine infections, and the estrogen responsible for stimulating some mammary tumors. The only caveat here, as with any steroid medication, is that liver values may be elevated in some individuals. These levels may be monitored in older bitches.