You can use any kind of cinnamon in small amounts for cooking, but for therapeutic use, consult a health provider and use Ceylon cinnamon from a reliable source.
Cinnamon is obtained from the inner bark of several tree species from the genus Cinnamomum. Cinnamon is used mainly as an aromatic condiment and flavouring additive in a wide variety of foods. The aroma and flavour of cinnamon derive from its essential oil and principal component, cinnamaldehyde.
Cinnamon is not only delicious, it has many reported health benefits. However, if you are using cinnamon for medicinal purposes, it should be Ceylon cinnamon, not Cassia, which is the common variety sold in grocery stores. Cassia cinnamon in large doses may have detrimental effects on health.