safest flea med? (prevention, medication, fleas, cheap)

[Hebrews12]

We have to board our indoor-only cats and the facility requires flea prevention. Our cats have never had flea meds/flea collar etc. What would be the least toxic flea medication (otc?). The facility would accept a collar but I can't guarantee it would stay on the cats and could be irritating for them (strong chemicals from the collar). I would need something that works short-term rather than a med that last for 6 mos and possibly have greater side effects bc I assume it's stronger (?). Cheristin is otc and seems to only last 6 wks.

Any ideas?

[Rene S]

FYI, I've heard that the cheaper and off-name brands (like Hartz) medications are much more likely to have side effects and products.

Since it's just for one month, I'd choose something that's been around for a while, like Frontline or Revolution. Read the packaging if you only want to buy something for fleas, because it seems there are several versions these days.

If you want to double check, you can always ask your vet too.

[evening sun]

Ask your vet. They will sell them to you