You have to get a prescription for chewables from the vet. Ours will do it but they don't like it. Beware vets that have impulse merchandise at the counter.
On a side note, there have been reports of dogs getting seizures from the chewables. Seizures that can continue after dosages stop. Lots of info online on this.
This is why I went with the Credelio. I did a lot of research before going to a prescription chewable. There are lots of bad reports of seizures, deaths and other non-desirable symptoms with Nexguard. That seems to be the worst one. I read the clinical trials and aftermarket reports on Credelio and it seems to be the one with the least bad reactions.
And it works.