Lithium increases gastrointestinal tract weight of male or female rats but it increases body weight only in females.

Lithium treatment of patients and laboratory animals causes increased body weight but no single organ or system has been found responsible. In the present work, we showed that lithium increased the weight of the female rat's gastrointestinal (GI) tract including its contents. The weight gain of the female rat GI tract was the same order of magnitude as the weight gain of the whole body of the females. All three parts of the GI tract (stomach, small intestine, colon) participated in the weight gain. Lithium treatment of male rats also increased GI tract weight, but lithium did not increase their overall body weight because of loss of weight at other sites.