 Crude coltar and its derivatives have been used in modern medicine for the treatment of psoriasis since at least 1925 as part of the Gokumen regimen. The mechanism by which coltar has its therapeutic effect is unknown, but polycyclic aryl hydrocarbons, specifically carbazol, are thought to be responsible for the treatment efficacy of crude coltar. Further research is needed to fully characterize the mechanism of action of crude coltar and create new therapies for psoriasis. This article was authored by Sahil Sikhon, Caleb Jorn, Myonokimura, and others.