As I have mentioned in previous posts, ALL of my business comes from people who have already used some sort of lice "shampoo" or treatment with little success. Doctors, pharmacists, and Alberta Health Services almost always recommend a permethrin based-treatment such as Nix or R&C. Once again, I recommend against the use of such treatments, and not just because permethrin is a pesticidal neurotoxin. I recommend against them because, in my experience, they don't work well.
I just came from yet another home that where a treatment was used on the child about 4 days before my visit. The parents thought that they had solved their child's lice problem, but they wanted me to check through the hair just in case.