Daly, P. A., Krieger, D. R., Dulloo, A. G., Young, J. B. & Landsberg, L. (1993). Ephedrine, caffeine, and aspirin: safety and efficacy for treatment of human obesity. International Journal of Obesity 17, S73-78.
In one phase of the above study participants used ECA for 5 months. One participant used ECA for 60 weeks w/o adverse effects (unless you consider losing 66.3 kg an adverse effect for an obese female!!)
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Theres a link to a very thorough article that deals more w/this written by a brilliant young man (heh heh heh).
J