The goal of any alleged fat loss compound is to increase the rate of fat loss. This can be achieved by increasing the overall metabolic rate, reducing the absorption of macronutrients during digestion, reducing the amount people eat, or increasing the rate at which fatty acids are released from fat cells. Some newer fat-burning compounds may also work via uncoupling, which is the process of creating heat from fatty acids inside a cell.
Most supplements sold for fat loss are either ineffective, insufficiently researched, or likely to be harmful. Stimulants can damage the cardiovascular system and cause sleep disturbances in high doses; increase the rate at which fatty acids are released from fat cells, which can worsen insulin sensitivity; and block the absorption of fats and carbohydrates, which can lead to unpleasant gastrointestinal symptoms. There may be some supplements that have meaningful effects with little downside, but this category of supplements should be used only with the utmost caution and scrutiny.