For IRS purposes, "distilled spirit"
mean that substance known as ethyl alcohol, ethanol, or spirits of
wine in any form (including all dilutions and mixtures thereof from
whatever source or by whatever process produced)
So it is a distilled spirit, with or without LSD, for those tax purposes. LSD is a controlled substance, see 21 USC 812
The key phrase here appears to be "dilutions and mixtures thereof". The term thereof would suggest that this phrase applies to mixtures of "distilled spirits", "alcoholic spirits" and "spirits" only, not to mixtures of these with some other substance.