Knowing Nixon, he probably recorded it, he did record a lot of things in the Oval Office. :blobcatgiggle:
That said, while Nixon himself didn't criminalizing cannabis or heroin, he did create the DEA for the sole purpose to heavily enforce existing drug laws (aka War on Drugs), but by the time the DEA officially started, Watergate had happened and Nixon was getting drunk, yelling at paintings, so the enforcement lingered until Regan came along in 1980.