Every few weeks, Dr. Tony Wing Lai Mak, a pathologist at Princess Margaret Hospital in Hong Kong, receives blood and urine samples from yet another patient hospitalized after taking a traditional Chinese medical or health supplement.

His toxicology lab finds the same culprits over and over: adulterants hidden in the dose.

Although the Hong Kong Department of Health regularly issues warnings about the medicines, “we’re still seeing this all the time,” Dr. Mak said.

“These are illegal products that are damaging to people’s health and can even kill. Yet somehow, they’re still here.”

The frequency and serious nature of the cases inspired Dr. Mak and his colleagues to compile a decade’s worth of observations, which they recently published in the British Journal of Clinical Pharmacology.