This is Dr. Christian. Welcome to JustAnswer. There are some hormone injections that might help stop the heat cycle but they are expensive and dangerous when used frequently. Unfortunately, cats go into heat often, as much as every 2 months so isn't a practical solution. Some people say that gently inserting a moist q-tip into the vulva (only a 1/4 inch or so) may stop the heat cycle but again this isn't ideal. Spaying is really the best long term option to prevent heat.
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