1P-LSD or 1-propionyl-lysergic acid diethylamide is a psychedelic drug of the lysergamide class that is an analog of LSD and homolog of ALD-52 and has been sold online as a designer drug since 2015.
While 1P-LSD shows only 38% the potency of LSD in mice, LSD is detected via LC-MS when 1P-LSD is incubated in human serum. This implies that 1P-LSD acts as a prodrug for LSD. This partially explains the effects of 1P-LSD, because the compound itself is unable to bind to the 5-HT2A receptors responsible for the effects of psychedelic drugs.
Prior to the publishing of the above cited research, pharmacologist David E. Nichols reportedly commented with his thoughts on 1P-LSD serotonin receptor binding:
The effects profile of 1P-LSD is not well defined. It is generally thought to be comparable to that of LSD.
1P-LSD is not scheduled by the United Nations' Convention on Psychotropic Substances.
1P-LSD is illegal in Denmark.
1P-LSD is illegal in Japan since 18 April 2016.
1P-LSD is illegal in Latvia. Although it isn't specifically scheduled, it is controlled as an LSD structural analog due to an amendment made on June 1, 2015.
1p-LSD is illegal in Lithuania.
1p-LSD is illegal in Finland.
1P-LSD is illegal in Sweden.
1P-LSD is illegal in Norway.
1P-LSD is illegal in Switzerland.
1P-LSD is illegal in the UK under the Psychoactive Substances Act.
While 1P-LSD is not controlled at the federal level in the United States, it's possible that 1P-LSD could be considered as an analog of LSD, in which case trade or possession with intent for human consumption could be prosecuted under the Federal Analogue Act.