A study of more than 8,700 men diagnosed with low testosterone found that those who received injections or other testosterone-boosting products were 30 percent more likely to suffer a heart attack, stroke, or death. Testosterone therapy can be a beneficial treatment, since low-T can cause a rise in plaque in the arteries, an increase in fat in the midsection, and higher blood sugar. "The danger comes when men who are not actually low on testosterone buy these supplements and obtain super high levels without a doctor monitoring them," says Dr. Larry Santora, medical director of the Dick Butkus Center for Cardiovascular Wellness in Orange County, California. "Men using these products need their levels monitored, as well as their blood pressure, blood sugar, and lipid levels."