The traditional Chinese medicine banlangen has once again come under the spotlight because of an outbreak of the H7N9 strain of avian flu that has infected 28 people and left eight of them dead, according to the country's health authorities. Banlangen, also known as Isatis root, from the biennial plant Isatis indigotica Fortunehas, has been used medicinally for about two millennia to reduce fevers and combat viruses. Banlangen was used in the fight against severe acute respiratory syndrome, or SARS, in 2003, when Zhong Nanshan, director of the Guangzhou Institute of Respiratory Diseases, recommended the herb as an antivirus medicine.

Since then, banlangen has been widely used and is said to have played an important role in preventing H5N1 avian flu and H1N1 flu over the past decade.

From a TCM viewpoint, banlangen is a cold compound that can dissipate heat, cool the blood and provide relief for sore throats and upper respiratory infections.

Pharmacological studies show banlangen has antibacterial and antiviral properties, is effective against Leptospira spirochaete bacteria, detoxifies, boosts the immune system, and kills off leukemia cells.

As production technology of the herb has progressed, it can be produced in more varied forms for consumption, such as granules and tonic drinks.

When H7N9 bird flu was first reported in early April, some health experts recommended banlangen to prevent further infections and the herb quickly sold out in pharmacies across the country.

Even so, there are doubts about the efficacy of the herb in combating H7N9 bird flu, and many experts are recommending that consumers do not take large doses over a long period of time, especially the elderly, pregnant women and children.

"Although banlangen does function as an antiviral, it has side effects and may cause allergic reactions," says Zhang Wei, a TCM expert in Shanghai.

Traditional Chinese medicine should be used under medical guidance and if not can have negative effects, he adds.

"Banlangen granules are a combination of several herbs," says Zhang Shunan, vice-director of the lung diseases department at China-Japan Friendship Hospital, a TCM practitioner, and executive director with the World Federation of Chinese Medicine Societies.

"It is a staple traditional Chinese medicine that has been used for colds and other ailments for ages, but it cannot be used as a universal preventive drug against the new bird flu."

Firstly, he says, there is no such thing as a TCM preventative prescription that works for everyone. This goes against the key doctrine of TCM that emphasizes personalized prescriptions for each individual, according to their situation.

Second, there are different types of colds and flus that are variously categorized as "cold-natured" and "heat-natured".

Banlangen only can relieve the symptoms caused by heat-natured diseases, Zhang says. "You can't simply say banlangen does or doesn't work against bird flu."

"Whether the herb can treat the disease or not is dependent on whether the disease is heat-nature based. It is not about the disease alone, it is related to the symptoms that are determined by the disease, the patient's physical condition, the environment and the weather, taken as a whole.

"If the patient's symptoms are caused by a bird flu that has a heat nature, banlangen can treat the disease, otherwise, it cannot."

Only a TCM practitioner can decide if banlangen is suitable for treating an ailment, Zhang insists, and if not the undesirable side effects can include discomfort to the digestive tract, especially children and the elderly.

In some extreme cases, banlangen may cause diarrhea and dehydration, Zhang warns.

"Additionally, it is nonsense to suggest that banlangen can boost the immune system. And if there is no disease, why bother to take medicines? It is like fighting an enemy that exists only in the imagination."

Ke Huixing, vice-director of the respiratory diseases department at Beijing Hospital, says: "To date there have been no clinical trials or observations confirming the efficacy of banlangen against the H7N9 virus."

Therefore, Ke suggests, people should not take the herb, unless directed to do so by a qualified TCM practitioner.

Doing so could affect the metabolism, including the digestive tract, kidney and liver. It will do more harm than good to take banlangen to prevent H7N9 bird flu infection if someone is healthy, Ke confirms.

"The government and experts should take responsibility to explain to the public that there is no need to panic."

Instead, Ke says people should keep fit to maintain their immune systems and be careful not to come into contact with infected poultry.