People who smoke shisha, or herbal tobacco, can suffer from high carbon monoxide levels, its research revealed.
It found one session of smoking shisha resulted in carbon monoxide levels at least four to five times higher than the amount produced by one cigarette.
High levels of carbon monoxide can lead to brain damage and unconsciousness.
Shisha is a water-pipe, popular in many Arab countries, in which fruit-scented tobacco is burnt using coal, passed through an ornate water vessel and inhaled through a hose.
The Department of Health said it was difficult to know exactly how much carbon monoxide one cigarette produced, due to the differences in smokers' inhalations.