context: Oregano is an herb that's commonly used in cooking. Oil extracted from its leaves has a long history of medicinal uses. Over the centuries, it has been used to treat a variety of ailments, including snake and spider bites, respiratory troubles, and menstruation problems. Today, it is marketed for the treatment of a long list of health conditions. There are many claims about the uses of oregano oil. But there is little evidence to suggest that it is effective for any condition. For example, oregano oil is often marketed for the treatment of intestinal parasites and the symptoms that go with it, such as: Bloating Cramping Constipation Diarrhea Fatigue A single study found that taking 200 milligrams of oregano oil three times a day for six weeks eliminated three such parasites. But the study was small, inconclusive, and was funded by a supplement manufacturer. Some laboratory studies show that oregano or its components have properties that can kill some food-borne germs. But there is no evidence that it helps prevent food poisoning. Oregano oil has also been used to treat a condition that some alternative medicine practitioners refer to as yeast hypersensitivity syndrome. In this condition, an excess of the yeast candida albicans is thought to cause symptoms, such as sinus congestion, headache, fatigue, and depression. It is not a condition that is recognized by conventional medicine. And there is no evidence that oregano oil helps treat these symptoms. Oregano oil in an oral or inhaled form is also used to try to treat respiratory tract conditions such as: Coughs Asthma Croup Bronchitis Oregano oil is also marketed as an aid for: Urinary tract infections Indigestion Heartburn Oregano oil, in a form that can be applied to the skin, has been used to try to treat: Acne Athlete's foot Dandruff Warts Gum disease Toothaches Skin infections Wounds Marketers of oregano oil claim a host of other applications as well. There is no human clinical research to back up these health claims. Optimal doses of oregano have not been set for any condition. Quality and active ingredients in supplements may vary widely. This makes it difficult to set a standard dose. Oregano leaves can be steeped in hot water and prepared as a tea. The concentration of active chemicals in oregano tea is markedly less than is found in the concentrated essential oil. Experts agree that oregano is safe when used for its intended purpose -- adding flavor to food. Oregano's safety for medicinal purposes is not known. Due to some of its properties, a few things should be kept in mind when taking oregano or oregano oil in medicinal amounts. In large doses, oregano oil may be toxic -- and even lethal. Oregano may have diuretic effects. Large amounts of oregano can upset the stomach. Oregano oil may cause rash when applied to the skin. Pregnant women should not take oregano in medicinal amounts because the oils the contain could reach the baby and harm it or may cause miscarriages. And people taking lithium should avoid oregano. You should also be very careful of using oregano oil if you are on blood thinners or medicines for diabetes. People should also avoid oregano if they have allergies to certain herbs such as: Basil Lavender Hyssop Marjoram Mint Sage Thyme Be sure to tell your doctor about any supplements that you take, even those that are labeled "natural."