Is dog flea and tick medicine, the kind that gets rid of fleas, ticks, lice and others ok for humans to use?
No. There are differences in the way humans metabolize and react to some drugs compared to animals.
Ivermectin.... ..Is off-label for human use - meaning it's not approved, but it's been used. Some breeds of dogs and cats are easily poisoned with ivermectin, so caution is in order for people.