EPHEDRA (Ma Huang) and ROOT (Ma Huang Gen) 
Ephedra is bitter, acrid, and warm in nature.
Class: Herbs that Release The Exterior
Family: Ephedraceae
Pharmaceutical Name: Ephedra Sinica
Parts Used: Herb
Dosage: 3-9 grams
I chose to do a quick write-up on Ma Huang because I have seen a variety of threads here and there about the herb (and topic) recently. Ma Huang is debatedly one of the most scrutinized and misunderstood Chinese herbs to date. It has continued to receive a good deal of publicity recently as some herbal suppliers carry it and others do not. As of 2006, the FDA is still pursuing against products that use the herb, and more specifically, isolated compounds and analogs of those found in the herb.
Chinese Ma Huang herb, originating in Mongolia, is one of a variety of species of this herb around the world. It operates on the lung and urinary bladder meridians, and like other herbs in this category, is often used to treat the eyes, ears, nose, and throat. It has the action of releasing the surface (exterior) by increasing surface cappilary circulation which induces perspiration. It also promotes the circulation of lung qi and promotes urination. Ma Huang is often used to relieve coughing, wheezing, and asthma, as well as clear edema. It is also indicated for what is called Tai Yang (Greater Yang) stage with chills, fever, and headache where there is a lack of sweating.
Ma Huang is often combined into traditional recipes such as Ephedra Tea Combination (Ma Huang Tang) to remedy chills, fever, headache, general aches, upper respiratory congestion, lack of sweating, or in TCM, a "thin and white" tongue with a "floating and tight" pulse. It is also combined with a variety of other herbs for the common cold, cough, asthma, or edema. Interestingly, ma huang is also an herb that is on occasion found in dit da jow recipes as well.
Of interesting note, the root of Ma Huang (Ma Huang Gen) works in exactly the opposite way from the herb, stopping sweating as a result of a yin deficiency (although herbs in the category of ma huang gen generally treat symptoms and dont address the specific deficiency) and to remedy spontaneous sweating, to include night sweats and postpartum sweating. The seemingly opposing actions in the same plant is a common theme among herbs of high potency and is a great illustration of yin and yang.
As can be seen from the above info, the ma huang herb is not supposed to be used as a diet aid. It was extracted and concentrated, and then packaged as a "stimulant" by the drug companies, which is where the abuse set in. Unfortunately, this has ruined it for the rest of us...
Ma Huang is contraindicated for those with high blood pressure, insomnia, or night sweating. It is not recommended for extended long term use.
Some info from the FDA:
http://www.fda.gov/oc/initiatives/ephedra/february2004/
A quick article addressing the active compound ehpedrine:
http://www.nycacupuncture.com/ephedra.html