People using cordyceps should take them in moderation - and inform their doctor if they take them regularly, experts have advised.
The warning comes after the case of a 58-year-old woman who underwent surgery for a benign brain tumour at Singapore General Hospital, and later died after developing extensive bleeding in the brain.
On Thursday, State Coroner Marvin Bay attributed Madam Chew Kim Kee's death last year to her failure to tell doctors that she had been taking cordyceps in the week before the operation.
The popular Chinese herb - a parasitic fungus - contains adenosine, which impedes platelets in the blood from clumping together and forming a clot, thus increasing the risk of bleeding.
The herb is traditionally used to boost a person's energy and strengthen his immune system.
It has been used to treat respiratory problems such as asthma and chronic bronchitis, and can be brewed in soups, ground into powder, or taken in tablet form.
It will not affect my choice to take (cordyceps), but I will definitely let my doctors know all the medications I take - especially if there is a major operation or lab test.
MS KAREN KAN
The coroner's inquiry found Madam Chew's death to be a medical misadventure. Although doctors had asked whether she had taken herbal medicine before surgery, she answered in the negative.
Her husband said this was possibly as she thought cordyceps was a health supplement, not a medicine.
Traditional Chinese medicine (TCM) experts told The Straits Times that cordyceps may interact with Western medicines in unpredictable ways.
For instance, cordyceps may augment the effect of warfarin - a commonly prescribed blood thinner for people with heart conditions.
Dr Lim Min Yee, a physician at Nanyang Technological University's Chinese Medicine clinic, added that the blood-thinning effects of cordyceps are not common, and may show up only in people with underlying medical conditions.
"Cordyceps when taken by healthy people as a dietary supplement are generally considered safe when used in accordance with proper dosing guidelines," Dr Lim said.
Physician Neo Min Jun, from the Eu Yan Sang Clinic, added that cordyceps are not suitable for those who are suffering from ailments such as flu, gastritis or high fever.
"It is a nourishing medicine and may not be suitable for all types of diseases," she said.
It is safe for a healthy adult to take between five and 15g of cordyceps a day, she added, although this may vary depending on a person's constitution.
In general, those who wish to start taking cordyceps regularly - especially pregnant women and children - should seek a TCM practitioner's advice beforehand.
Ms Chan Shu Ling, a sales manager, was concerned when she saw news of the death, as her mother- in-law takes cordyceps pills.
"She has a history of tuberculosis, and when there is haze she keeps coughing. But after she started taking cordyceps, her throat got so much better," she said.
Now, the 29-year-old said she will let her mother-in-law's doctor know that she is taking cordyceps whenever she goes for check-ups.
Administrative manager Karen Kan, 42, said:"It will not affect my choice to take (cordyceps), but I will definitely let my doctors know all the medications I take - especially if there is a major operation or lab test."