Quassia is a bitter wood from the Quassia and Picrasma tree genera. People take it as a digestive bitter to stimulate appetite and increase stomach acid and bile secretion. Historically, it was used for intestinal parasites, though modern evidence is limited.
Most people take quassia as a tea, tincture, or extract right before a meal. The intense bitterness also makes it a flavoring for drinks.
High doses can cause vomiting and nausea. Pregnant or breastfeeding women should avoid quassia because it may stimulate the uterus. People with stomach ulcers or gallbladder issues should be careful. Allergic reactions are rare but possible.