Although 1/3 of patients lose weight well with simple phen-pro, 2/3 of them lose only some of their excess weight and then get "stuck". When one asks them about it, many of them say that although the basic phen-pro suppressed their appetite well in the beginning, after a few weeks or months, their excess appetite spartially returned. If one adds 5-HTP to the mix at that point, the extra hunger goes away again and the patients resume their weight loss.