Trioxsalen (trimethylpsoralen (TMP), trioxysalen (INN) or Trisoralen) is a furanocoumarin and a psoralen derivative.

It is administered either topically or orally in conjunction with UV-A (the least damaging form of ultraviolet light) for phototherapy treatment of vitiligo[1] and hand eczema.

[2] After photoactivation it creates interstrand cross-links in DNA, which can cause programmed cell death unless repaired by cellular mechanisms.

[3] The compound is also being explored for development of antisense oligonucleotides that can be cross-linked specifically to a mutant mRNA sequence without affecting normal transcripts differing at even a single base pair.

[4] Trioxsalen (abbreviated as TMP) activated by UV-A exposure is commonly used in genetics research as an experimental mutagen.