Hi Warren – That depends on your tolerance and your pre-workout powder. If you are taking a pre-workout that contains caffeine or other stimulants I would be careful. Many of our customers take Hydroxyelite instead of their pre-workout, but you need to be mindful of the serving size and your tolerance. It is a good idea to start with a 1/4 or 1/2 serving of the fat burner to gauge your tolerance to the supplements effects. If you don’t get jittery and/or feel fine you can probably take 1 capsule. Under no circumstances would I suggest you exceed the daily suggested serving size set by the manufacturer. If you take a non-stimulant based pre-workout I think you should be fine, but again I would assess tolerance and first.