Complex sentence: Leary, Richard Alpert (later Ram Dass), Smith, and Weil-who were involved with the experimentation with and research of psychedelic drugs in the early 1960s.
Split into simpler sentences: Leary, Richard Alpert (later Ram Dass), Smith, and Weil. They were involved with the experimentation with, and research of, psychedelic drugs in the early 1960s.