Complex sentence: Osmond had become interested in hallucinogens and their relationship to mental illness in the 1940s and during the 1950s he made extensive studies of a number of drugs including mescaline and LSD.
Split into simpler sentences: Osmond had become interested in hallucinogens and their relationship to mental illness in the 1940s. During the 1950s, he completed extensive studies of a number of drugs, including mescaline and LSD.