Beasley B L, Nutt J G, Davenport R W, Chase T N
Arch Neurol. 1980 Mar;37(3):155-6. doi: 10.1001/archneur.1980.00500520053008.
The effect of 2 to 6 g of tryptophan per day on levodopa-induced psychiatric symptoms was tested in nine patients with Parkinson's disease in a double-blind, placebo-controlled trial. The psychiatric disturbances were not greatly altered by administration of tryptophan.