To quote one of my threads:
Ephedrine inside the body produces Noradreneline (NA) which then attachs to the beta receptor which in turn stimulates the G Protein. The alpha subunit attachs to the enzyme Adenylate Cyclase and activates it. The adenylate cyclase continues to produce Cyclic Adenosine Monophosphate (cAMP) which contines down the thermogenic pathway. There are a couple roadblocks to prevent this from happen. NA's productions is inhibited by prostanglins which is where the aspirin comes into play. Aspirin works to inhibit the production of prostanglins allowing for NA to be produced in a greater quanitity. cAMP is also inhibited by phosphodiesterase (PDE). That is where caffeine plays its part, caffeine inhibits PDE activity allowing cAMP to go down the thermogenic pathway.
You could use it while bulking but it's rather counter productive to cut and bulk at the same time.