What is the best shampoo for severe dandruff?

Several.: For most patient, alternating a zinc pyithione shampoo (head and shoulders) and a tar shampoo (neutrogena-t-gel), gives better results. Selenium shampoos work well and are an alternative. Finally, there are shampoos with salicylic acid, which is keratolytic, meaning it helps break apart scales. Finally, ketoconazole shampoo, ie. Nizoral, is quite beneficial.