Wellington, New Zealand ? A single joint of marijuana obstructs the flow of air as much as smoking up to five tobacco cigarettes, but long-term pot use does not increase the risk of developing emphysema, new research suggests.

The study by New Zealand’s Medical Research Institute found that longtime pot smokers can develop symptoms of asthma and bronchitis, along with obstruction of the large airways and excessive lung inflation. The paper was released Tuesday ahead of its publication in the journal Thorax.

“The study shows that one cannabis joint causes a similar degree of lung damage as between 2.5 and five tobacco cigarettes,” said lead author Sarah Aldington.

However, the researchers found that the progressive chronic lung disease emphysema, often associated with cigarette smoking, was uncommon among marijuana smokers. Only 1.3 percent of the long-term pot smokers were found to have signs of the disease compared with 16.3 percent of those who combined marijuana and tobacco, and 18.9 percent of those who only smoked tobacco.

Marijuana smokers had symptoms that included wheezing, coughing, chest tightness and phlegm – all of which were associated with tobacco smokers, except chest tightness.

Last week, another study published in The Lancet medical journal suggested that using marijuana may increase the likelihood of becoming psychotic, with even infrequent use potentially raising the overall small risk by up to 40 percent.