Ozone therapy has potentially serious adverse effects and at least five deaths had been reported as a result of the therapy's use on people with cancer. In Germany from 1975 to 1983, research revealed six deaths, four cases of visual disturbance, three cases of paraplegias, four gas embolisms in the pulmonary circuit, two heart attacks, four pulmonary embolisms, two cases of apoplectic paralysis, and two cases of abnormal heart rhythm following ozone therapy. More commonly, pulmonary edema is the most prevalent adverse effect of ozone treatment. In the muscular system, many cases of tendon rupture, osteoarthritis, myositis, synovitis, joint infections, and muscle tears have been documented results of ozone therapy. In the integumentary system, benign skin discoloration is most common. These all occurred following direct injection of O2/O3 gas, a method now regarded as malpractice by most (though not all) ozone practitioners. In each case, the clinical picture corresponded either to gas embolism or allergic shock. The fact that one case of apparent allergic shock followed injection of a very small quantity of gas raises the unknown possibility that other methods of administration might also carry a risk of allergic shock.