Malathion
"I needed three treatments two years ago (one week between each treatment), but the biggest problem is the dosage. This tiny bottle barely cover my scalp and does not reach anything near half-way down my 30" hair. Length and thickness of hair should be factors in the amount prescribed. I think the bugs just ran down to dryer hair to escape the poison. Still, it worked better than OTC meds, which did nothing at all for the strain of lice I had. The directions I was given said to use half a bottle then use the other half a week later. A full bottle didn't even dampen my hair; half a bottle would have been less than useless."