WebMD explains that there are numerous tranquilizers that are deemed safe for cats over the course of short-term use, but they need to be obtained through a veterinarian. Tranquilizers are used to relieve anxiety in a frightened cat that is unused to potentially traumatic experiences, such as kenneling, travelling or visiting the vet.
According to WebMD, tranquilizers work by blocking the cortical inhibitory impulses, which can have an adverse reaction in some cats. Potential side effects include a failure to use the litter box or aggression, so use is recommended only when sedation is needed. The website lists Promace as one of the most effective drugs to reduce anxiety in cats while suppressing their pain center. However, it can have serious side effects and should not be used long term.
WebMD also recommends Valium, a drug popular among human and cat behavioral therapists for reducing anxiety and promoting relaxation. All Feline Hospital notes that Benadryl can be used as a feline sedative as a last resort as cats are generally opposed to the over-the-counter medicine's taste. Since Benadryl can easily be obtained at the store, it is a popular option for those who do not have time to get a sedative from the vet before going on a trip with their cat.