This is the third adaptogen that I am reviewing — I’m starting to suspect that adaptogen may indicate a herb that alters gut bacteria by reducing those that produce stress chemicals. There is no effective medical definition of adaptogen so inclusion is largely by popular allegation. Tinospora cordifolia [Guduchi], Asparagus racemosus [ a species of asparagus], Emblica officinalis[ Indian gooseberry], Withania somnifera[Ashwagandha], Piper longum[Indian long pepper] and Terminalia chebula were deemed to be adaptogens in Adaptogenic properties of six rasayana herbs used in Ayurvedic medicine
Rhodiola rosea L. modulates inflammatory processes in a CRH-activated BV2 cell model.  – “counteract the neuroinflammatory effect ” Implies reduction of brain fog and cognitive issues.
Rhodiola Rosea has a short monogram available with several reviews finding contradictory results.
- Like prior ones, it reduces oral bacteria: [Use of a golden root (Rhodiola rosea) tincture in treating periodontosis] 1981,
- Improves some memory, Effects of alcohol aqueous extract from Rhodiola rosea L. roots on learning and memory 
- Decrease in the level of psychic fatigue and situational anxiety, [The effect of the preparation rodakson on the psychophysiological and physical adaptation of students to an academic load]. 
- Anti-arrhythmia, [Mechanism of the anti-arrhythmic effect of Rhodiola rosea extract], [The anti-arrhythmia action of an extract of Rhodiola rosea and of n-tyrosol in models of experimental arrhythmias]., [The anti-arrhythmia effect of Rhodiola rosea and its possible mechanism].
- Anti-depression Clinical trial of Rhodiola rosea L. extract SHR-5 in the treatment of mild to moderate depression.
- ” concluded that repeated administration of R. ROSEA extract SHR-5 exerts an anti-fatigue effect that increases mental performance, particularly the ability to concentrate, and decreases cortisol response to awakening stress in burnout patients with fatigue syndrome.” A randomised, double-blind, placebo-controlled, parallel-group study of the standardised extract shr-5 of the roots of Rhodiola rosea in the treatment of subjects with stress-related fatigue.
- Anti-inflammatory activity of Rhodiola rosea–“a second-generation adaptogen”.
Dosage: ” indicating that the intake of 2 capsules after breakfast is more effective than the intake of 1 capsule after breakfast and 1 after lunch.” Efficacy and tolerability of a Rhodiola rosea extract in adults with physical and cognitive deficiencies  which also stated “statistically highly significant improvement in physical and cognitive deficiencies” (in other words some improvement). “Rhodiola extract at a dose of 200 mg twice daily for 4 weeks is safe and effective in improving life-stress symptoms to a clinically relevant degree” Therapeutic effects and safety of Rhodiola rosea extract WS® 1375 in subjects with life-stress symptoms–results of an open-label study.
Comment: While I have often used this, both Ashwagandha and Magnolia Bark seem to have significiant greater impact on me.