Please define what a "natural energy drink" is. Caffeine is actually a natural ingredient found in nature.
With that being said each one of us, depending on genetics and overall health react differently to different compounds. Scientific research has proven that white males, black males and asian males all react differently to certian types of yohimbine.
Moroever, overall health has an effect on the effectiveness of individual compounds found in energy drinks. A lean, healthy, athletic male will most definelty respond better to "natural" compounds than will an over weight, sedentary male with a poor diet. Its all about absorption rates and once absorbed how well the body processes it.
Furthermore, the quality of the active ingredient and its overall molecular structure is a huge determining factor in the effectiveness of any compound.
Whether you think can or think you can\'t, you\'re probably right!