Yup, you lose weight. It should be fat if you are eating right (enough protein, enough cals) & doing your lifting. Since your HR is speeded up, your metabolism is faster.
I've always had the impression it was more dangerous for those with High Blood Pressure & risk for heart disease.
Do some searches on Elite - also read the "ECA" post here on the Women's board by 'New@GettinBig' - Great info! ECA is ephedra, caffine, aspirin - ephedra is the same as ma huang.
I would say get as lean as you can with a clean diet & sound training program before taking something that is risky & potentially damaging to your body. THere are no short cuts & no substitutes for a healthy diet anyway.