A study in female cats showed that a 9.4 mg deslorelin implant (a GnRH‑agonist similar to triptorelin) blocks reproduction for about two years, works the same whether placed on the back or near the belly, and is fully reversible with no obvious side effects, though most cats gained weight.

Deslorelin is a GnRH-agonist used off-label for contraception in female cats. Little is known about duration and safety of the 9.4 mg subcutaneous implant in the queen as well as its efficacy when placed periumbilically. Fourteen female cats were administered the 9.4 mg deslorelin implant (during interestrus or anestrus) either in interscapular (N = 8) or periumbilical (N = 6) sites, following general and reproductive examination, vaginal cytology, hematology, biochemistry and progesterone assay to ensure health status. All above procedures (except for progesterone assay) were repeated weekly during the first month, then every 2 months until 6 months and then every 6 months until treated cats regained full reproductive function. No side effects were observed in any treated queen. Post implantation estrus occurred in 40 % of the subjects. A significant increase in body weight was observed during treatment (12/14 queens gained weight), particularly at the end of the study. At the end of the study some queens mated, conceived and kittened, proving reversibility of the treatment. The average duration of action of the 9.4 mg deslorelin implant was 790 ± 155 days (range 525-1140 days) with no significant difference in duration or efficacy depending on implantation sites. The 9.4 mg deslorelin implant causes pharmacological sterilization for about 2 years in female cats, is fully reversible and caused no clinically relevant side effects when administered at both interscapular and periumbilical sites.