JWH-203 (1-pentyl-3-(2-chlorophenylacetyl)indole) is an analgesic chemical from the phenylacetylindole family that acts as a cannabinoid agonist with approximately equal affinity at both the CB1 and CB2 receptors, having a Ki of 8.0 nM at CB1 and 7.0 nM at CB2.

It was originally discovered by, and named after, John W. Huffman, but has subsequently been sold without his permission as an ingredient of synthetic cannabis smoking blends.

[3][4][5] Unexpectedly despite its weaker CB1 Ki in vitro, the 2-methylindole derivative JWH-204 is actually more potent than JWH-203 in animal tests for cannabinoid activity, though it is still weaker than JWH-249.

[6] In the United States, JWH-203 is a Schedule I Controlled Substance.

[7] As of October 2015, JWH-203 is a controlled substance in China.