Caffeine is a highly common natural ingredient used in fat burning supplements. For this reason, many of the side effects observed from taking fat burners are similar to those experienced after consuming too much caffeine. These include Abdominal pain, Nausea, Anxiety. Generally, the ingredients in fat burners are safe for daily consumption but dosage requirements should be followed carefully to avoid any negative side effects. All products sold on A-List Nutrition include a detailed nutritional panel so check your chosen product carefully if you have any sensitivities.