APA (7th ed.) Citation

Cowen, P., Parry-Billings, M., & Newsholme, E. (1989). Decreased plasma tryptophan levels in major depression.

Chicago Style (17th ed.) Citation

Cowen, P., M. Parry-Billings, and E. Newsholme. Decreased Plasma Tryptophan Levels in Major Depression. 1989.

MLA (9th ed.) Citation

Cowen, P., et al. Decreased Plasma Tryptophan Levels in Major Depression. 1989.