During a 12-wk drug monitoring study, the efficacy and safety of a Rhodiola rosea extract given in combination with vitamins and minerals (vigodana(R)) were tested in 120 adults (83 women and 37 men, ages 50-89 y) with physical and cognitive deficiencies. Two different dosage regimens were chosen. One group of 60 patients (group 1) took 2 capsules orally in the morning after breakfast, and the other group (group 2) took 1 capsule after breakfast and 1 after lunch. Three medical examinations were performed during the course of the study (at baseline, after 6 wk, and after 12 wk). The evaluated symptoms were divided into physical disturbances such as exhaustion, decreased motivation, daytime sleepiness, decreased libido, sleep disturbances, and cognitive complaints (eg, concentration deficiencies, forgetfulness, decreased memory, susceptibility to stress, irritability). A statistically highly significant improvement (P<.001) in physical and cognitive deficiencies was observed in the overall group, as well as in the separately evaluated groups 1 and 2. In addition, the time needed to complete a digit connection test decreased significantly in all groups (P<.001). Improvements in group 1 were more pronounced than in group 2, however, indicating that the intake of 2 capsules after breakfast is more effective than the intake of 1 capsule after breakfast and 1 after lunch. Global assessment of efficacy revealed that treatment was "very good" or "good" for 81% of patients, as reported by physicians, and for 80%, as reported by patients. Ninety-nine percent of patients and physicians rated safety as "good" or "very good." No adverse events occurred during the course of the study. The results of this drug monitoring study are very promising, but they still need to be corroborated by future placebo-controlled clinical trials.
http://www.ncbi.nlm.nih.gov/pubmed/17901042
Rhodiola Rosea definitely improves my cognition and energy, but tolerance sets in after about 3-4 weeks. This study found no tolerance to the beneficial effects of Rhodiola. Perhaps it's due to the brand? Most Rhodiola brands are standardized to either 3% Rosavins or 3% Rosavins and 1% Salidroside. Rosavins are inactive; Salidroside and Tyrosol are regarded to be the main constituents that provide the beneficial effects of Rhodiola.
The brand I was taking was NOW Foods, which is standardized to 3% Rosavins and 1% Salidroside. The NOW Foods website mentions nothing of its Tyrosol content.
