Blood-thinning effect:
Chamomile is known to contain small but significant amounts of a chemical called coumarin. Coumarin, which has a pleasing fruity aroma, is known to act as a blood thinner. It is chemically very similar to coumadin, a synthetic chemical sold under the name Warfarin, as a prescription blood thinner.
Although the effects of a single cup of chamomile tea are small, chamomile is best used with cautiong by any people for whom a blood-thinning effect could be harmful or undesirable, especially those who are taking prescription blood thinners.
Allergic reaction:
Chamomile is in the composite family, related to asters and daisies, and as such, is relatively closely related to a large number of allergens, including ragweed and mugwort. Although uncommon, there are documented cases of cross-reactivity between these plants and chamomile. This means that a person who has never been exposed to chamomile but who is allergic to these other plants, or other plants in the composite family, has a small chance of reacting to chamomile in a similar way. Although rare, a few severe allergic reactions have been documented.
For this reason, chamomile is best used cautiously by people the first time they are exposed to the plant, among people who are at risk of severe reactions to plants in this family.
Chamomile is generally healthy:
Although this article has focused primarily on side-effects and potential health risks associated with chamomile tea, these risks and side effects are relatively insignificant compared to those of many prescription drugs. Chamomile is also known to have a number of compelling health benefits, including lowering blood sugar, and having a relaxing effect.
In summary:
Chamomile tea is safe and widely-consumed as a beverage. However, there are a few points of concern with respect to potential side effects or negative effects on health. The first is due to the fact that chamomile contains a chemical known to act as a blood thinner, and the second is due to possible allergic reactions due to cross-reactivity. Chamomile is thus best used with caution among people for whom blood thinning effects could be dangerous, and among people at risk of severe allergic reaction to plants in the composite (daisy or aster) family.
