JWH-251 (1-pentyl-3-(2-methylphenylacetyl)indole) is a synthetic cannabinoid from the phenylacetylindole family, which acts as a cannabinoid agonist with about five times selectivity for CB<sub>1</sub> with a K<sub>i</sub> of 29 nM and 146 nM at CB<sub>2</sub>. Similar to the related 2'-methoxy compound JWH-250, the 2'-chloro compound JWH-203, and the 2'-bromo compound JWH-249, JWH-251 has a phenylacetyl group in place of the naphthoyl ring used in most aminoalkylindole cannabinoid compounds.
In the United States, all CB<sub>1</sub> receptor agonists of the 3-phenylacetylindole class such as JWH-251 are Schedule I Controlled Substances.