Lester Grinspoon gives an interesting insight describing the hippie movement of the 1960’s in terms of earlier bohemian cultures with the added component of LSD–a psychedelic experience once limited to a select few in a larger community.

The hippie movement constituted the mass following of the psychedelic ideology. It began to gather force around 1965 and reached its height between 1967 and 1969. Although the matter was often obscured for tactical reasons, there is no doubt that the initiating element, the sacrament, the symbolic center, the source of group identity in hippie lives was the psychedelic drug trip. To drop out, you had to turn on. It was not a question of how often the drugs were used; sometimes once was enough, and many people experienced a kind of cultural contact high without taking drugs at all.

Earlier bohemians had their unconventional dress, sexual and work habits, hairstyles and political attitudes; what distinguished hippiedom and expanded its population far beyond that of genuine literary and artistic bohemias was simply the extra ingredient of LSD. By democratizing visionary experiences, LSD made a mass phenomenon of attitudes and ideas that had been the property of solitary mystics, esoteric religions, eccentric cults, or literary cliques. Every teenager who had taken 500 micrograms of LSD could convince himself, with the help of teachers like Timothy Leary, that he was in some sense an equal of the Buddha or Einstein.

From Psychedelic Drugs Reconsidered (Grinspoon, 1979)