Side effects of chamomile are very minimal unless an individual has an allergy to it. Always consult your physician before trying any new type of food or supplement, including chamomile. If you have an allergy, you should consult an allergist. People are more likely to experience an allergic reaction to chamomile if they have an allergy to such plants as ragweed, chrysanthemums, marigolds, or daisies. Very high concentrations of chamomile may cause nausea and vomiting. Also, chamomile is a natural blood thinner, meaning that if you take blood thinner medications, it is probably best to stay away from chamomile tea.