A sixth person died on Wednesday as officials urgently try to find out what killed them.
New York’s state health department said “Dank Vapes” and “Chronic Carts” contain vitamin E acetate, a thickening agent in THC oil – the psychoactive compound in cannabis.
A study in the New England Journal of Medicine found 24 of 41 people with the lung illness reported using Dank Vapes.
The effect of vitamin E acetate on the lungs in unclear and the US Food and Drug Administration has advised people to stop vaping THC oils and using unofficial products sold outside of shops.
The Dank Vapes brand uses diluted THC oil, but it is unclear whether it is made by one producer or is a name used by multiple manufacturers.
Drug dealers have been diluting THC with vitamin E acetate to maximise their profits.
Cannabis extracts in vaping pens have been one of the biggest growth segments in the US states which have legalised the drug.
The US Centers for Disease Control and Prevention is investigating hundreds of confirmed or probable cases of lung illness connected to vaping.
However, it says the condition has not yet been definitively tied to one product or ingredient.
Patients tend to arrive at hospital coughing and short of breath, with many also having a fever, general fatigue or gastrointestinal problems.
It has not been unusual for the patients to be put into intensive care units and on ventilators.
The increase in cases has prompted a Congressional hearing to be scheduled on the matter for later this month.
Products branded under the Dank Vapes name were until recently available on Amazon and are still for sale elsewhere on the internet.
Recognised makers of nicotine e-cigarettes, such as Juul Labs, British American Tobacco and Imperial Brands have said their products do not contain THC or vitamin E compounds.