I've had my 12yo Lab on Comfortis for 3 months now. Zero side affects. He takes it with a meal, stomach's it just fine and is flea and tick free
It really helped him get over a flea allergy he developed in his senior years.
PROBLEM: Its not for dogs under 5 pounds.
BE CAREFUL when considering for your Yorkie! For your bigger furbabies you might consider it.