Possible side effects of Floyd Nutrition ZXT Slim, marketed as an all-natural dietary supplement, include increased risk of heart attack, stroke and cancer. These side effects are caused by two active ingredients, sibutramine and phenolphthalein, that are not listed on the product's label, reports the Food and Drug Administration.
Other common side effects of sibutramine include anxiety, constipation, vertigo, dry mouth, headache, runny or stuffy nose and difficulty sleeping, according to Drugs.com. Less common side effects of this drug include diarrhea, dehydration, drowsiness, abdominal, stomach or back pain, irregular heartbeat, edema of the body, feet or ankles and depression. The Food and Drug Administration classifies sibutramine as a controlled substance.
Common side effects of phenolphthalein include burping, diarrhea, stomach cramps, rash and discoloration of the urine, says WebMD. Phenolphthalein was available over the counter in the United States until the FDA reclassified it as generally unsafe because it poses a cancer risk and may cause genetic mutations.
In 2008, the FDA launched a campaign against weight-loss products and diet supplements contaminated with prescription drugs and chemicals. In April 2015, the FDA and the Department of Justice, jointly filed a criminal investigation with the Harrisburg, Pennsylvania, U.S. District Court that charged the owner of Floyd Nutrition with selling misbranded drugs.