is caffeine an appetite suppressant
While caffeine has long been used as an appetite suppressant, in this study it was decaffeinated coffee that resulted in significantly lower hunger levels and higher plasma levels of PYY than placebo (plain water) and the other caffeinated beverages.
When a diet pill contains green tea extract, supposedly, the extract is the polyphenols from the green tea leaves. In addition to EGCG and its benefits -- including increased metabolism -- green tea also contains caffeine, which is said to be a mild appetite suppressant.