Fat burners are dietary supplements that claim to help you lose weight by increasing your metabolism and burning fat. While they may be effective in helping you reach your weight loss goals, there are potential risks associated with taking them. Fat burners These include increased heart rate and blood pressure, insomnia, headaches, jitteriness, anxiety, nausea and vomiting. Additionally, some fat burners contain stimulants like caffeine or ephedrine which can cause addiction if taken in large doses over a long period of time. It is important to speak with a doctor before taking any kind of supplement as it could interact negatively with other medications or conditions you may have.