I have been using the supplement Rhodiola for fatigue and mental fatigue. What I can say is that the research is great for fatigue. I can also say that at my dose of 105mg I do see the benefits to it, but I believe it would be better twice a day. It seems to help after I take it for a certain duration and then I slump again. Although, with both fibromyalgia and migraines I can see why I would need an additional boost. Nevertheless, it is noticeable which is rare for supplements.
Research suggests that it significantly reduces fatigue. And that in people who are fatigued helps with cognition issues, related to the fatigue… in other words, clears up the mental fatigue cloud. For a daily preventative of fatigue, it can be beneficial in as low a dose as 50 mg. “Rhodiola can improve cognitive functioning in persons who experience a reduction in fatigue, but there is insufficient evidence to support an outright increase in cognition (which should occur in non-fatigued persons)” Examine.com
In one study: “The study was carried out on a highly uniform population comprising 161 cadets aged from 19 to 21 years. All groups were found to have very similar initial data, with no significant difference with regard to any parameter. The study showed a pronounced antifatigue effect reflected in an antifatigue index defined as a ratio called AFI. The verum groups had AFI mean values of 1.0385 and 1.0195, 2 and 3 capsules respectively, whilst the figure for the placebo group was 0.9046. This was statistically highly significant (p < 0.001) for both doses (verum groups), whilst no significant difference between the two dosage groups was observed. There was a possible trend in favour of the lower dose in the psychometric tests”