Rhodiola is one of my favorite botanicals! In fact, it was one of the first Western botanicals that I studied way back in the day (the 90's). One of the reasons I was so intrigued with this herb, was because of its versatility and powerful therapeutic effects. 30 years later, and I'm still in awe of this herb, and recommend it to many of my patients, who after using it, are just as amazed.
The patients I usually recommend this botanical to, have succumbed to the heavy effects of stress; whether it be from work, school, caregiver stress or any other type of stress that takes its toll on the body and mind.
The most common symptoms reported by these patients are:
What is rhodiola?
Rhodiola belongs to a special class of herbs known as adaptogens, which includes other famous herbs like, Siberian Ginseng (Eleuthero) and Astragulus.
The term "adaptogen" was introduced during the 50's by the Russian Toxicologist Nicolai Lazarev, who was studying substances that could prevent fatigue and increase resistance to physical and mental stress.
According to Nicolai Lazarev, “an adaptogen is a pharmacological substance capable of inducing in an organism a non-specific state of increased resistance enabling it to counteract stress signals and adapt to exceptional effort.”
Lazarev's pioneering work was heavily influenced by Hans Selye, the scientist who developed the stress model, “General Adaptation Syndrome”, which describes the effects of stress on the human body. 
When we are faced with "danger" or any type of stressor, our sympathetic nervous system (SNS) goes into over-drive and initiates the "fight" or "flight" response, which gives us that energy boost (adrenaline) to over -come the situation. The parasympathetic nervous system (PNS) is supposed to calm us down after the danger / stress has passed. The problem for most people, especially Westerners, is that we are stressed all the time. We have become a chronically over-stimulated society that runs on stress, essentially suppressing the (PNS) and never giving it a chance to do its job and calm us down.
Adaptogens to the rescue! Through the use of an adaptogen like rhodiola, we are able to take the edge off and help even the score between the (SNS) and the (PNS). Rhodiola increases the body’s resistance to stressors, restores balance to the nervous system and allows the body to heal itself.
How does rhodiola work?
Rhodiola rosea L. contains a variety of compounds ranging from antioxidants and organic acids to flavonoids, but the constituents that are responsible for its adaptogenic properties are: Rhodioniside, rhodiolin, rosavin, rosin, rosiridin, salidroside (synonym: rhodioloside and rhodosin) and p-tyrosol.
Based on a vast accumulation of data, rhodiola works primarily through the central nervous system. Much of this activity occurs along the hypothalamic-pituitary-adrenal (HPA) axis, which moderates the body’s “fight” or “flight” response to acute stress. 
In the brain, rhodiola is able to alter chemicals in the brain by inhibiting monoamine oxidase (MAO) A, which is a gene that contributes to the development of depression. 
Rhodiola can reduce the amount of cardiac damage caused by stress by modulating the release of neurotransmitters like cortisol and cyclic-AMP in the heart. 
By improving cerebral blood circulation and brain metabolism rhodiola can increase concentration and memory , as well as, protect against fatigue / burn-out and increase mental performance through the influence on the HPA axis, moderating certain survival proteins that are activated under stress, and altering levels of nitric oxide, which regulates physiological functions and aids in cellular metabolism. 
The Remarkable Three
The majority of the studies used a dosage of 200mg - 400mg. per day. Manufactures normaly put 100mg in a capsule and recommend that it be taken 2-3 times per day.
The dosage recommended on the manufacturers bottle should be followed, but one thing to keep in mind is that dosages may need to be modified depending on one's weight, age, gender metabolism and whether the stress is acute or chronic.
Always consult with your practitioner before taking a supplement, there can be drug-herb and herb-herb interactions.
Contraindications & Adverse Reactions
Herb - Drug Interactions