Illegal anti-impotence drugs and herbs contaminated with the diabetes drug glyburide have caused some 150 cases of dangerously low blood sugar, researchers in Singapore reported on Wednesday.

Four people have died, they said in the New England Journal of Medicine.

The drugs include counterfeit Cialis and herbal preparations with names such as "Power 1 Walnut" and "Santi Bovine Penis Erecting Capsule," Shih Ling Kao of National University Hospital said.

The packaging listed fictitious overseas factories as the manufacturer, "so it is not known whether there was deliberate or accidental contamination," they wrote.

All but one of the 150 victims were men, ranging in age from 19 to 97.

"We believe that physicians should be cognizant of this phenomenon when evaluating patients with severe unexplained hypoglycemia, particularly if a clustering of cases is noted," Kao's team wrote.