Essiac tea can cause the side effects of nausea and vomiting, states the National Cancer Institute. Essiac is an herbal tea that is used by some to treat cancer, diabetes, AIDS and gastrointestinal diseases.
Essiac tea reportedly contains burdock root, Indian rhubarb root, sheep sorrel and the inner bark of slippery elm, according to the National Cancer Institute. Supporters of the product say the combination of herbs strengthens the immune system and has anti-inflammatory effects. As of 2015, no clinical trials have confirmed these claims. Essiac tea is sold as a health tonic, but is regulated as a food substance by the Federal Drug Administration and not approved by the entity to treat or prevent disease.