Arsenic trioxide, which was approved for medical use in 2000, is a medication used to treat a type of cancer known as acute promyelocytic leukemia. This drug basically interferes with the growth and spread of cancer cells in the body, even though its mechanism of action is still not completely understood. It is worth noting that Arsenic trioxide is given as an infusion into a vein. On a side note, you may need frequent medical tests to be sure this medicine is not causing harmful effects. You may also be given other medications to help prevent serious side effects or allergic reaction. As for the side effects of Arsenic trioxide, they include vomiting, diarrhea, swelling, shortness of breath, and headaches. In addition, this medication can cause serious side effects such as APL differentiation syndrome and heart problems. Bear in mind that both men and women using Arsenic trioxide should use effective birth control to prevent pregnancy. In fact, this drug can harm an unborn baby or cause birth defects if the mother or father is using it.