Black walnuts have been used to treat everything from parasites to acne for centuries. While few scientific studies have been done on side effects of black walnuts (Juglans nigra), those with nut allergies or who are pregnant might want to steer clear of drinking tea made from the towering tree's leaves or bark.
Black walnut trees grow throughout the world and can be found in the eastern half of the U.S. Ancient Greeks reportedly treated intestinal problems with black walnut, and in traditional Chinese medicine consuming the nut is thought to build strength. Throughout the centuries, black walnut tea has been used to treat gout, rheumatism and parasites; however, few scientific studies have been done to validate health claims or determine possible side effects, according to the American Cancer Society.
Some people are allergic to walnuts and can have potentially life-threatening reactions as airways close and their lips and tongue swell. Others who are allergic might experience gastrointestinal upset. Those who have experienced allergies to other tree nuts, especially pecans, should be careful when consuming walnuts, as they might have a reaction, warns the American Cancer Society.
Black walnuts contain high levels of a chemical called tannins. Tannins might affect the way certain prescription and nonprescription medication is metabolized in the body. Do not consume black walnut tea while taking codeine, theophylline, ephedrine or pseudophedrine, Drug Digest warns. Iron supplements also might interact with the tannins in black walnuts.
Kidney, Liver and Intestinal Concerns
Chemicals in black walnuts could irritate the kidney and liver, and those with kidney and liver conditions should not drink tea made from the nuts, according to Drug Digest. In addition, tannins in high doses can stimulate strong bowel activity and should be avoided by pregnant women and those with chronic gastrointestinal conditions.