It's an adaptogenic herb, extremely good for dealing with stress and fatigue (which is a form of stress).
It's not a stimulant. It works by increasing the body's resilience to stressors. I like to say it makes you "more healthy than healthy."
Modern science has a hard time proving the effectiveness of herbal supplements for the simple reason that it isn't designed to do that.
In health, research studies are fairly simplistic in design. People are either sick or healthy, based on some predetermined range of clinical measurements. The studies have no ability to resolve differences of health state within the range that is considered "healthy." Everything in the healthy range is valued the same. So how do you measure something that makes you "more healthy than healthy?"
What adaptogens do is increase your ability to stay in the "healthy" state under stress from outside factors. Science can't measure this, because adaptogens don't make you better when you are sick. What they do is stabilize your system so you are less likely to succumb to stressors that might make you sick, be it a cold or high blood pressure.
Does that make sense?
In any case, I did my homework as I always do and if you want a good OTC source of Rhodiola that is a great value, go with THIS ONE.
During my eight (8) year tenure in R&D at the vitamin company, I had access to a clinical grade of Rhodiola plus Ginseng from Australia, where herbals are clinically tested the same way that pharmaceuticals are here.
It's hard to find good quality Rhodiola in our sloppily regulated supplement industry. But Rhodiola should contain at least 3% rosavins and 1% salidrosides in the Rhodiola rosea extract.
THIS PRODUCT (Solaray's Super Rhodiola) has all the elements of a good source of the herb and gets great ratings - 4 to 5 stars out of 5, consistently.
That would be my recommendation. Label claims also suffer from a dearth of validation in the United States, but if customers consistently report good results, it's probably a decent product.
If you can get your hands on some of the Australian Rhodiola, manufactured by MediHerb and sold via health care practitioners ONLY, then do that. But it will cost you, so I still recommend the Solaray Rhodiola for a cost effective source.