Pregnant or breastfeeding women may need to be especially cautious. Some herbs that are safe for most people might cause a reaction in your body. Among those reported to occasionally induce reactions are chamomile, cayenne, echinacea, garlic, kava kava, kelp and valerian. Be alert for unusual symptoms such as rash, nausea or upset stomach, especially when first starting a remedy. If you think you're having an allergic reaction, stop taking the herb and talk to your doctor immediately.
Most herbs are safe when taken as directed.
A good guideline is to avoid combining an herb with similar-acting drugs or herbs. For the same reason, people with hemophilia in particular should not use garlic and ginkgo together. On the other hand, some herbs may counteract the negative effects of certain drugs. For instance, milk thistle can reduce liver damage from several toxic drugs while not interfering with their therapeutic action. If possible, seek out those who are also knowledgeable about pharmaceuticals, especially anti-HIV medicines.