Educational information, not medical advice — ask your doctor or midwife.
Gyepi is the dried inner bark of the cassia cinnamon tree (Cinnamomum cassia). It is used as a single herb in Korean traditional medicine. Healers call it a warming herb and give it for cold hands and feet, a cold or weak stomach, and period pain.
You may already know it as the kitchen spice cinnamon. The bark used in cooking and the bark used in herbal medicine are the same, but herbal doses are larger and taken more often.
Human trials have mostly looked at blood sugar in type 2 diabetes, and the results are mixed and weak. Long use in Korean medicine tells you the herb has standing, not that it works; the two are separate things, and this page reports both.
Nobody has shown for certain how Gyepi acts in the body. Lab work points to a compound called cinnamaldehyde, which gives the bark its smell and taste.
In test tubes and animals, cinnamon extracts seem to help cells take in sugar and to slow how fast the gut breaks down starch. Whether this happens at the doses people actually take is not clear.
Korean tradition explains it in its own terms, as an herb that warms the middle of the body and moves blood. That is a traditional idea, not a measured effect.
Gyepi comes in several forms:
Dried bark quills or chips, simmered in water to make a decoction (a strong tea made by boiling).
Ground powder, used in food and in herbal formulas.
Capsules and tablets of powdered bark or extract.
Water or alcohol extracts sold as liquids.
Cinnamon essential oil, which is very strong and is meant for scent or diluted skin use only, never for swallowing.
In Korean clinics Gyepi is more often one part of a mixed formula than a herb taken alone.
Cinnamon bark has been traded and used as medicine for well over two thousand years. It appears in Korean medical texts such as the Donguibogam (1613) and in the older Chinese herbal tradition Korean medicine drew from.
It is also a staple in Chinese medicine as rou gui, in Ayurveda as twak, and in old European and Arabic medicine. Few herbs are so widely shared across traditions.
See a doctor right away if your skin or the whites of your eyes turn yellow, your urine turns dark, or you get pain in the upper right of your belly. These can be signs of liver trouble.
Get urgent help for a swollen mouth, lips or throat, a spreading rash, or trouble breathing after taking it.
Call your doctor if you bruise or bleed more easily, or if your blood sugar drops low with shaking, sweating or confusion.
Book a normal appointment if your digestion, period pain or cold hands and feet do not improve, get worse, or are new. Do not use Gyepi in place of medicine you have been prescribed.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
Reviewed by the HealisticMD editorial team How we grade evidence →
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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