The asprin is used to prolong/delay the effects of the e&c. You will get much the same effect without it but it will be more intense and not as long lasting. So if you are using it for a fat burning effect it is good to have the A added in. If you are looking for a boost for a workout and not the longer effects on bf then just go with the e&c. There is an article on the mag that goes into this. I cant remember which one but you can find it by searching for ECA on the mag.