How often should i retreat lice with over-the-counter medication?

Just one retreatment: For head lice, treat every affected person on the same day. Remove all the bugs and nits from everybody's hair. Just using the medication (such as nix (permethrin)) is not enough . . . One must remove the bugs and nits. Each day, check everybody's hair for remaining nits to remove. After 7-10 days, treat with nix (permethrin) again, and do hair checks every day for one week after that. Then, do hair checks occasionally.

Give it a week: I commonly retreat any infestation a week after primary treatment to catch any stragglers that may have been missed or emerged from eggs in the interim.