Fat burners increase your deficit so you can more easily lose fat. Less cals also means more of a chance of fat loss. Without hormonal support you will be more likely to lose muscle. This is especially true with T3. T3 burns fat and muscle. If you use it on cycle, the gear helps to protect muscle but in PCT and right after, when you are must sensitive to muscle loss, it could be much worse. So be very careful if you do this. You could get just clen and run that at 20-40 through PCT but I would not want to use T3 in PCT and off gear in general.