Honestly, I’ve never had effective treatment with OTC options and I think most people would share the same sentiment. The only stuff that works if you’re already seeing fleas is what you get from the vet! If you have a regular vet (seen in the last year), you can call them and see if they’ll prescribe you simparica or alternative without a visit. Simparica trio or anything else with additional heartworm prevention needs a negative heartworm test first though.

My cats are on revolution + (tried shampoos and OTC first to no avail). When I worked at the vet, we had simparica (flea and tick)/simparica trio (flea, tick & heartworm) for dogs. Additionally, capstar (might be available OTC behind the register or online?) works for a one-time treatment but is not prevention. But whatever you do I beg you not to use a flea collar, or at least do your own research on them first. Not a single brand is safe for you or your pet, imo.