Rou Gui (肉桂; Ròu Guì; Latin: Cinnamomi Cortex; English: cassia bark / Chinese cinnamon bark) is the dried bark of Cinnamomum cassia Presl. In Chinese medicine it is an interior-warming herb. It is acrid, sweet, and greatly hot, enters the Kidney, Spleen, Heart, and Liver channels, and its core actions are to supplement fire and assist yang, conduct floating fire back to its source, disperse cold and relieve pain, and warm and unblock the channels. It is not Gui Zhi. The twig is acrid-warm and stays closer to the exterior; it releases the muscle layer and unblocks yang. The bark is greatly hot and holds in the interior; it supplements Ming Men fire. It is not Ceylon cinnamon (Cinnamomum verum). Culinary bark is not this official drug. The smell is thick. In a decoction it should be added late, or taken as a small powder. The dose stays small.

It is used most often for three patterns:

• Kidney-yang deficiency / Ming Men fire decline — impotence, cold uterus, cold low-back and knee pain, wheezing from Kidney deficiency
• Floating deficiency yang — cold below and heat above, red face, dizziness; fire must be conducted home
• Cold congealing with pain — cold pain in the heart or abdomen, cold shan, painful or absent periods, deficiency-cold vomiting and diarrhea

The usual decoction dose is 1–5 g. As powder, 0.5–1.5 g. Yin-deficiency fire, reckless hot blood, and pregnancy are contraindications or strong cautions. Greatly hot and acrid-sweet, it is not dessert cinnamon to dust on food every day at bark doses.

When the lower origin is cold, or deficient fire floats, cold loins and knees with a red face and cold feet are common. Rou Gui is acrid, sweet, and greatly hot. It tonifies, conducts home, and unblocks, which is why it appears in Shen Qi Wan, You Gui Wan, and Gui Fu Li Zhong Tang. It supplements fire more than it nourishes yin. A dry red tongue, night sweats, and a sore throat get worse if more heat is added.

Rou Gui is not a catch-all for feeling cold or “warming the Kidney,” and kitchen cinnamon is not a stand-in for Ming Men-level use. In yin-deficiency fire or excess-heat constipation, using it alone can assist fire and stir blood. Bark or twig, and whether to add it late, should be decided by a licensed Chinese medicine practitioner after pattern diagnosis.

1. Historical Records

• Shen Nong Ben Cao Jing: Noted its use for clearing upper respiratory issues, soothing the throat, benefiting the joints, and tonifying Qi.
• Ming Yi Bie Lu: Highlighted its ability to treat heart and rib pain, warm the meridians, unblock blood vessels, and induce sweating.
• Xin Xiu Ben Cao: Expanded its uses to warming the middle, treating cold-induced headaches, and lower back pain. It also explicitly warned that it could cause miscarriage.
• Ben Cao Gang Mu: Summarized its effectiveness in treating cold-damp joint pain, loss of voice, and cold-type diarrhea.
• De Pei Ben Cao: Emphasized its powerful combinations, noting that pairing it with Shu Di (Prepared Rehmannia Root) nourishes the Kidney fire, while pairing it with Ren Shen (Ginseng) secures the body's foundational energy.

2. Evolution of TCM Understanding

Different TCM practitioners throughout history have utilized Rou Gui for varying core purposes:

• Tonifying Yang: Some focus on its ability to rescue extreme Yang deficiency and boost foundational energy.
• Dispersing Cold: Others rely on its warming power to unblock stagnant Qi and relieve cold-induced pain in the meridians.
• Safety Boundaries: Later physicians emphasized its "hot and drying" nature, firmly warning that people with "Yin deficiency and excessive fire" (those who run hot and dry) should never use it alone, as it can severely deplete the body's moisture.

1. Main Chemical Components

Modern analysis shows that Rou Gui (Cinnamon Bark) is rich in volatile oils—primarily cinnamaldehyde—as well as diterpenes, flavonoids, and coumarins.

• Lab Observations: In vitro studies suggest that cinnamaldehyde may have anti-inflammatory and antioxidant properties.
• Animal Studies: Extracts have shown potential in improving energy metabolism in animal models. However, comprehensive human clinical trials are still needed to confirm these specific effects.

2. Modern Pharmacological Focus

Current scientific research is heavily focused on the herb's volatile oils. Researchers are exploring how these compounds might regulate inflammatory responses, modulate the immune system, and influence energy metabolism. While promising, the research remains largely in the exploratory phase.

3. Limitations of Modern Research

• Animals Aren't Humans: Promising results in a petri dish or in mice do not automatically translate to the same therapeutic effects in the human body.
• Extracts vs. Whole Herbs: Modern lab studies often use isolated, highly concentrated compounds (like pure cinnamaldehyde). This acts very differently from a traditional water decoction of the whole bark.
• Methodology Gaps: Discrepancies in extraction methods and dosages across different studies make it hard to form a single, unified scientific conclusion.
• The Holistic Effect: TCM relies on the synergistic effect of the entire plant. Judging the clinical value of Rou Gui based solely on one isolated chemical ignores the complex way the whole herb interacts with the body.