Phentermine is one of the worst stimulants when it comes to your heart. When I was on it, my BP was always over 110/minute for the 4 months I was prescribed it. It's actually one of the most cardiotoxic stimulants. I would avoid this drug if you could. It's nice because it will last you all day (though that could be because I was Rx'd #2 37.5mg of it, and you know I took it all at once, and when my tolerance got high, I would take 3-4 at a time. Snorting them make them hit harder, but they don't last much time at all. Maybe 3 hours of strong stimulation, followed by several hours of extremely mild stimulation.
P.S. If you're prescribe it, it's one of the higher priced drugs as insurance won't cover it, and it's in such high demand.