Tranquilizer, Sedative - Yarrow also contains a small amount of hypnotic chemical, thujone, the effects of which have been compared to marijuana. The thujone in Yarrow may account for its traditional use as a sedative. In large amounts, thujone is poisonous, but recommended amounts of Yarrow do not contain enough to cause harm. Yarrow may also be useful as a urinary antiseptic for fighting infections such as cystitis. Common useful forms of Yarrow are tinctures and teas.
Some people develop an allergic rash if they handle the fresh herb in sunlight.
Yarrow may also interfere with the absorption of iron and other minerals. At least one in three Americans use some sort of herb or herbal formulation for health purposes and in many other parts of the world this ratio is even higher. Herbs are advertised for their preventative qualities and effectiveness, such as avoiding memory loss, curbing stress, fighting colds, relieving pain, or even improving the quality of sleep. Roughly 25 percent of pharmaceutical drugs have herbal origins. Though many herbs are not as potent as traditional drugs, they still contain some of the same active ingredients as drugs, plus they often contain other ingredients, some of which may have different functions or may even be toxic.