You can safely take 8mg of ephedrine every 4 to 6 hours. This is for the standard HCI dosage. If you want to do a stack dosage, then you can safely take 20 mg of ephedrine, 200 mg of caffeine, and 80 mg of aspirin. Make sure you do a test dose first to ensure that you react to it okay. You should be careful when mixing with other pre-workout supplements as they often have caffeine, and mixing caffeine with ephedrine is where you could put yourself at a serious health risk. If used correctly, ephedrine can have an impact on your fitness goals in a positive way.