TFA does say so:

> During the following 10 years or so, Sacks took a prodigious amount of amphetamines and psychotropics – “every dose an overdose” – with one trip producing visions of the “neurological heavens” so intense it inspired him to write his first book, Migraine (1970).

That time frame matches the NPR episode you cited:

> One chapter, called "Altered States," described his own experiments with mind-altering drugs in the '60s when he was a neurology resident.