I have been using this forever with my animals. Lex gets a tablet per day of the Brewers Yeast W/Garlic. He has yet to have a flea or tick on him. My old cat who used to like to go outside...same thing never had a problem. I don't use any other flea and tick preventative.
I get a 1000 table bottle from :
www.jefferspet.com
It's the Four Paws Brewers Yeast With Garlic.
I personally get it this way and have never mixed or tried to combine two pills. It's funny because I always used this for their coats and then later found out about it's usefulness as a flea/tick deterrent. I was on another chat and mentioned it only to find out that two other breeders on there use the same for their pets and nothing else.
Good luck. Jeffers is a great place to buy thing. I have been buying from them for years now.