Artemisinin is a sesquiterpene lactone with an endoperoxide bridge and has been produced as an antimalarial drug. The efficacy of tea, made with either water or urine and "A. annua", for the treatment of malaria is dubious, and is discouraged by the World Health Organization. Research has found that artemisinin is not soluble in water and the concentrations in these infusions are considered insufficient to treat malaria. A 2012 review stated that artemisinin-based remedies are the most effective drugs for the treatment of malaria. A 2013 review suggested that although "Artemisia annua" may not cause hepatotoxicity, haematotoxicity, or hyperlipidemia, it should be used cautiously during pregnancy due to a potential risk of embryotoxicity at a high dose.