The spice derived from a tropical tree’s bark and used to help lower blood sugar is cinnamon.
Cinnamon is made from the dried inner bark of several trees in the genus Cinnamomum. Farmers harvest young branches, remove the outer bark, and allow the inner bark to curl into quills as it dries. Two widely traded types are Ceylon cinnamon, Cinnamomum verum, and cassia cinnamon, which comes from several related species.
Cinnamon has long been used in traditional medicine, including preparations intended to support digestion and blood-sugar control. Modern studies have investigated whether cinnamon supplementation affects fasting blood glucose, insulin resistance, or HbA1c. Some reviews report modest improvements in fasting glucose, but results vary by species, dose, preparation, and study quality.
That uncertainty matters: cinnamon should not replace prescribed diabetes treatment. Large amounts of cassia cinnamon may also provide substantial coumarin, a compound associated with liver toxicity. In normal culinary quantities, however, cinnamon is primarily a flavoring used in foods and drinks around the world.