First of all one reason I hesitated trying anything like this before was expecting it to feel like over caffeinated jittery anxiety. This does not feel like that even when you take the second one 4 hours after the first. I've taken it a few days now. The first two days just one capsule and the second two one capsule in morning and another 4 hours later as directed. Very easy to tolerate and don't notice any unpleasant effects. They do seem to make me slightly more alert. I haven't noticed the heat sensations I've seen in other logs but will keep at it and religiously report my observations. So far work outs seem unaffected. Basic full body every other day. I'm going to be trying to add time to cardio and see if the Pyro RX seems to make that any easier than usual. I haven't eaten as much but I'm not sure if it's this or being crazy busy.