These were the ONLY things that worked for my flea problem this year (for my indoor cats - San Francisco had a real insane flea infestation this summer). The stuff the vet recommended was useless. I kept them snug but not at all tight - the cats didn’t like them for the first hour and then forgot about them.
There are some weird spiky things on the collars when you open them up, I think to keep them together in the packaging - CUT THESE OFF before putting them on the pets. I read a bunch of scary reviews of poisoning and it seems a lot of the issues were from pets getting poked by the spikes (the package says to remove before putting them on - be sure to follow this advice).
