ALD-52, also known as N-acetyl-LSD, is a chemical analogue of lysergic acid diethylamide (LSD). It was originally discovered by Albert Hofmann but was not widely studied until the rise in popularity of psychedelics in the 1960s.

In TiHKAL, Shulgin touches briefly on ALD-52 in entry 26, LSD. His writings are vague, second hand accounts, saying doses in the 50-175 µg range have resulted in various conclusions. One found that there was less visual distortion than with LSD and it seems to produce less anxiety and was somewhat less potent than LSD. Another report claimed it was more effective in increasing blood pressure. Yet another could not tell them apart.

It has the same characteristics as LSD, but supposedly "without the anxiety, tenseness, and other problems inherent to it".

In The Hallucinogens by Hofmann and Osmond (1967), ALD-52 (D,L-acetyllysergic acid diethylamide) is listed as having a lower (approximately ¹/₅) intravenous toxicity (in rabbits), a lower (approximately ¹/₈) pyretogenic effect, an equal psychological effect in humans, and double the "antiserotonin" effect as compared with LSD.