Reported side effects from Artemisia annua include stomach pain, a slowed heart rate (bradycardia), diarrhea, nausea, vomiting, decreased appetite, and flu-like symptoms. However, since many of these adverse effects were reported in clinical studies for malaria, it's not clear whether these were symptoms of malaria or side effects caused by the herb.[1][2] Additionally, Artemisia annua has allergenic pollen which has been reported to cause dermatitis (rash) and other allergy symptoms in susceptible individuals.[2]
There have been rare reports of liver toxicity with Artemisia annua. In one case report, 1.25 grams of Artemisia annua powder had been consumed daily for 4 weeks.[3] In another case report, 600 mg of artemisinin (extracted from Artemisia annua) had been consumed daily for 10 days.[4] A case series reported liver toxicity in 29 adults who had taken Artemisia annua supercritical carbon dioxide extract in grapeseed oil,[5] although it was criticized for having poor reporting methods and confounded causality testing.[6]
Artemisia annua should not be used during pregnancy, as animal research shows that it has toxic effects on the embryo/fetus.[7]