I think maybe some over the counter dewormers are good...I just like the ease of Interceptor.....the package claims to contain the common worms, plus heart worm..so that's why I like it. It can be purchased online, etc.....but because it is for heartworm, you wouldn't want to just start it without first testing. For months I used an over the counter dewormer for Addie.....prior to heartworm testing, and she never had worms. That kind of tells me it worked. I had even been using an 'off' brand....Earliworm....or something like that..don't know the manufacturer name offhand...been so long ago. The vet I went to then wouldn't even look at your pet prior to a worm test......so I'd say the OTC ones worked!