I have read every kerouac bio except Amburn's and other recent ones.
I think you can find it in Nicosia's. Perhaps Charters.
There is no mention of drug taking by Jack after 1962 ( Leary's mushrooms ) . In his last years ( 1964-1969 ) I don't believe he did anything other than booze . If you can find contradictory info in Charters' or Nicosia's books please let me know . My best to you ...