t3 and clen are much stronger than anything you can buy at GNC...that is why they are illegal! However, this strength is also countered by the possibility of Hear problems (clen) and thryoid problems (t3) - and believe me you don't want either of those. It's important that you use them respondibly.
BTW their risks are highly debated, just do a search. Some people say they can really fuck you up, others say it's bogus. You really have to decide for yourself. Either way, I would start with conservative dosages.
Also, don't run this if your looking to drop 5-10lbs. I would only use this stuff if I was training to cut very seriously with dedication. Don't play with your body.