Nytol sleeping tablet on top of its box. Nytol is a brand name for diphenhydramine, which belongs to a class of drugs known as sedating histamines. It is used for the temporary relief of sleep disturbances and can be bought over the counter. As well as decreasing the time it takes to fall asleep, nytol also increases the depth and quality of sleep. If taken in large doses it has hallucinogenic effects.