Italian researchers conclude that licorice even in the small amounts eaten by many people can cause a significant drop in testosterone levels in men and this in turn can result in a loss of libido and other sexual dysfunctions. Licorice is widely used as a flavouring agent in candies, breath mints, and throat lozenges. The active ingredient in licorice, glycyrrhizic acid, has strong hormonal effects and can block the conversion of androstenedione to testosterone. Researchers at the Universities of Padua and Sassari report that men who eat licorice may lower their testosterone levels enough to decrease their libido (sex drive). The experiment involved seven normal young men who consumed seven grams of a commercial licorice preparation daily for seven days. The glycyrrhizic acid content of the licorice tablets was 0.5 gram. The men had blood samples drawn at the start of the experiment, four days and seven days into the experiment, and four days after its conclusion. The average serum level of testosterone before licorice ingestion was 740 ng/dL; after four days it had dropped to 414 ng/dL, and after seven days it was 484 ng/dL. The value four days after cessation of licorice intake reverted back to normal (704 ng/dL). Licorice consumption has also been linked to the development of hypertension.
Armanini, Decio, et al. Reduction of serum testosterone in men by licorice. New England Journal of Medicine, October 7, 1999, p. 1158 (letter to the editor)