Fowler's solution is a solution containing 1% potassium arsenite (KAsO2) which was first described and published as a treatment for malaria and syphilis in the late 1700s and was once prescribed as a remedy or a tonic.<ref>Template:Cite journal</ref><ref name=Jolliffe>Template:Cite journal</ref> Thomas Fowler (1736–1801) of Stafford, England, proposed the solution in 1786 as a substitute for a patent medicine, "tasteless ague drop". From 1865, Fowler's solution was a leukemia treatment.<ref name=Jolliffe/><ref name=Doyle>Template:Cite journal</ref>
From 1905, inorganic arsenicals like Fowler's solution saw diminished use as attention turned to organic arsenicals, starting with Atoxyl.<ref name='ITOM'>Template:Cite book</ref>
As arsenical compounds are notably toxic and carcinogenic—with side effects such as cirrhosis of the liver, idiopathic portal hypertension, urinary bladder cancer, and skin cancers—Fowler's solution fell from use. In 2001, however, the U.S. Food and Drug Administration (FDA) approved a drug of arsenic trioxide to treat acute promyelocytic leukaemia,<ref>Template:Cite journal</ref> and interest in arsenic has returned.<ref>Template:Cite journal</ref>