Lysergic acid propylamide (LAP), also known as N-propyllysergamide (NP-LA), is a serotonin receptor modulator of the lysergamide family related to lysergic acid diethylamide (LSD). It is the analogue of LSD in which the N,N-diethyl groups have been replaced with an N-propyl group and is also the N-propyl derivative of ergine (lysergic acid amide; LSA).
It was initially reported that LAP was inactive as a hallucinogen in humans but produced autonomic effects at relatively low doses in both animals and humans, with no other details, such as doses, provided. Subsequently, Alexander Shulgin reported that LAP was inactive at a psychedelic at doses of up to 500üg and had at least less than 20% of the hallucinogenic potency of LSD.
The drug had about 40% of the antiserotonergic activity of LSD in the isolated rat uterus in vitro. The potency of LSD analogues in this assay increased with length or size of the monoalkyl chain: ergine (4.3%) < lysergic acid methylamide (6.3%) < lysergic acid ethylamide (11.9%) < lysergic acid isopropylamide (22.2%) < LAP (40.0%) < lysergic acid butylamide (64.9%) < lysergic acid amylamide (75.1%). However, activity in this assay does not correlate with hallucinogenic activity.
LAP was first described in the scientific literature by Albert Hofmann and colleagues by 1955.