Western research labels ma huang an "adrenergic bronchodilator".  That is, it opens up the bronchial tree by stimulating the sympathetic nervous system.  It shrinks congested mucous membranes, helps dry up the watery discharge and opens stuffed nasal passages which accompany the common cold or flu and bronchial asthma.  It is also considered to be a central nervous system stimulant, precipitating sweating and urination.

Traditional contraindications for ephedra include general weakness, poor digestion, high blood pressure, nervousness, sleeping difficulties, cardiac arrhythmia, heart disease, hyperthyroidism, and difficult urination caused by prostate enlargement.  Some believe it may also contract the uterus, making it inadvisable during pregnancy.  It's also recommended that ma huang/ephedra not be used with certain prescription drug MAO (monoamine oxidase) inhibitors such as isocarboxacid, phenelzine, or tranylcypromine and even possibly the now popular St. John's Wort (hypericum perforatum).  These substances can potentiate the stimulating effects of ephedra.

A physician properly trained in the use of Chinese herbs takes into account the patient's overall physical condition and appropriateness before this herb is prescribed in combination with other herbs to enhance its effectiveness and buffer any reaction.  Normal prescription dosages are in the range of 3-9 grams of ma huang/ephedra per prescription, consumed over 2-3 times per day.  This equates to approximately 180 - 540 mg of ephedrine in a day.  In humans, an estimated 50% of the oral dose is excreted in the urine in the first 3-4 hours, 88% is excreted within 24 hours, and 97% after 48 hours.  Chinese herbal preparations are recommended to be taken 2 or 3 times daily.  Thus, additional doses of the ma huang containing formula are taken when only proportionately smaller amounts of ephedra are in the system.

Ma Huang
Ephedra Controversy
Governmental Intervention
Effective Uses of Ma Huang
Personal Notes on Ma Huang