This is a great product. I always have a great workout when using this. But be warned - check with your physician if you are using this for a long period. Stay hydrated and use wisely. If you notice increased heart rate or dizziness call your Dr! There's quite a bit of caffeine in here and if your getting it elsewhere as well, you need to adjust your intake. It's a great product, you simply have to listen closely to what your body is telling you.