Common medicines to protect dogs and cats against fleas and ticks are causing them to develop tremors, seizures, or lose control of their movements, the Food and Drug Administration has warned.

FDA officials are alerting pet owners and veterinarians to be on the lookout for these potential side effects in the drugs, which pets take about once a month. The side effects have been observed in the medicines Bravecto, Nexgard, and Simparica.