They work well if you dog already has fleas to get rid of the fleas, but you need to use a flea pipettes to actually kill the fleas for a month.
Although you need to put the dog out or we found the fleas would try to jump off them onto us.

When I gave him capstar my dog spent the rest of the afternoon throwing up. I notice he wasn’t scratching but the next day he was didn’t do anything only for the first day. It’s expensive & I won’t get again as he was so sick