All my dogs get NexGard all 12 months to prevent fleas, ticks. They also all get HeartGard all 12 months for heart worm, worm prevention. Kai is 5 now and has been on them for all 5 years, our terrier for almost 8 years. We have been fortunate not to have any ill effects from them. My daughter is switching to Bravecta for Kai only because its taken every 3 months and she says it gives her more time to save the $$ for it.