Why has veterinarian prescribed Megestrol Acetate on animals?

　　Megestrol acetate(CAS.NO 595-33-5) is used to postpone estrus and alleviate false pregnancy. It may be used in cats to treat behavior problems (e.g. inter-male aggressive behavior, urine spraying, aggression towards people). It has also been used to treat a variety of skin conditions.

Megestrol acetate,595-33-5

　　How do you give this medication?
　　*Give this medicine to your pet as directed by your veterinarian. READ THE LABEL CAREFULLY.
　　*If the medicine is a liquid, measure the dose with reasonable care.
　　*Try to give this medication at about the same time each day.
　　*DO NOT give your pet more medicine than directed and DO NOT give the drug more often than directed
　　*DO NOT stop giving this medication to your pet unless directed by your veterinarian.
　　*Try not to miss giving any doses.
　　What if I miss giving a dose?
　　Give the dose as soon as possible. If it is almost time for the next dose, skip the missed dose, and continue with the regular schedule. Do not give the pet two doses at once.
　　How do I store this medicine?
　　*Keep this medicine out of reach of children
　　*Store this medicine in a cool, dry place at room temperature.
　　*Do not store this medicine in the bathroom, near the kitchen sink or in damp places. The medicine may break down if exposed to heat or moisture.
　　What are the potential side effects?
　　*The following side effects have been reported: excessive thirst, excessive urination, personality changes, drowsiness, and increased weight. In dogs, changes in hair color may occur.
　　*Notify your veterinarian if mammary changes or if side effects are noted.
　　*Other side effects may occur. If the pet experiences anything unusual, contact your veterinarian.