Rhodiola has been studied extensively for its anti-fatigue abilities. In 2000, a double-blind, placebo-controlled study was published examining the effect of rhodiola on students during a stressful examination period. This test found rhodiola to improve mental fatigue and neuro-motoric tests, however, it didn’t prove to be effective in other tests, such as a correction of text test and a neuro-muscular tapping test. A more recent study published in 2009 determined rhodiola helped individuals with stress-related fatigue. They showed better results than the placebo group in tests administered to determine fatigue and ability to concentrate.

Although most tests have showed positive or mixed results, a double-blind, placebo-controlled study on military cadets aged 19 – 21 didn’t find a significant difference in the effect or rhodiola vs placebo in mental ability tests; however, it did show a significant improvement in the mood and feelings of well-being for the cadets taking rhodiola.

A recent study published in the Journal of Sport and Health science tested the effects of Rhodiola on a group of 26 healthy young men. They performed tests to determine whether the herb would affect reaction time and endurance. During psychomotor testing, the rhodiola group performed superior to placebo in reaction time and total response time. This study did not show any improvement in endurance for the men taking rhodiola.

One of the most encouraging clinical studies was performed on 56 young, healthy physicians. This 6-week test used a “Fatigue Index” test to determine the overall level of mental fatigue, involving complex perceptive and cognitive cerebral functions, such as associative thinking, short-term memory, calculation and ability of concentration, and speed of audio-visual perception. Physicians were tested before and after night duty. The doctors showed better scores during the time-period when they were taking rhodiola than they did during the time period they were taking placebo (this was a crossover study).

Several studies have looked at the effect of 200mg Rhodiola on physical activity and endurance. A four week study found that participants in the Rhodiola group had improvements in VO2 max. This finding indicates that Rhodiola may improve exercise capacity (1).

A study that looked at the effect of Rhodiola on c-reactive protein. Study participants underwent exhausting physical exercise tests on a computer-aided bicycle ergometer. The group that received 340mg Rhodiola extract (containing 30mg of active substances) twice per day had lower levels of c-reactive protein and creatine kinase five days after exercising. The placebo group had higher levels of both markers. The findings indicate that Rhodiola may impact recovery rate by exerting an anti-inflammatory effect (2).

60 people suffering from stress-related fatigue volunteered to participate in a double-blind, placebo-controlled clinical trial. The subjects were given 576mg of rhodiola or a placebo for 28 days. The test showed that rhodiola lowered cortisol levels, high cortisol levels are a significant marker of stress.

A 2007 clinical trial recruited volunteers suffering from mild to moderate depression. This 6-week trial on 89 subjects found that the group receiving rhodiola experienced improvements in mood and emotional stability, along with less insomnia and somatization, but rhodiola did not improve self-esteem.

Rhodiola has been studied recently for its benefits in sports nutrition. A 4-week study in 2004 found some mixed results. This double-blind, placebo-controlled study found improvements in the VO2 max for the rhodiola group compared to placebo; however, it found no changes in muscle strength, speed of limb movement, reaction time, and attention.

Another study in 2004 found positive results for rhodiola as an anti-inflammatory after exercise. This study put 36 untrained, healthy volunteers through exhausting physical exercise tests carried out on a computer-aided bicycle ergometer. The group being given rhodiola showed lowered levels of c-reactive protein and creatine kinase after 5 days of exercise, whereas the placebo group experienced higher levels of the inflammatory markers. These results are encouraging towards rhodiola improving recovery rate.