Methoxsalen (marketed under the trade name Oxsoralen) is a drug used to treat psoriasis in conjunction with exposing the skin to sunlight. Methoxsalen modifies the way skin cells receive the UVA radiation, allegedly clearing up the disease. The dosage comes in 10mg tablets, which are taken in the amount of 30mg 75 minutes before a PUVA light treatment.

Patients with high blood pressure or a history of liver problems are at risk for inflammation and irreparable damage to both liver and skin. The eyes must be protected from UVA radiation. Side effects include nausea, headaches, dizziness, and in rare cases insomnia.

Author John Howard Griffin used the chemical to darken his skin in order to investigate racial segregation in the south. He wrote the non-fiction book Black Like Me about his experiences.