TUESDAY, July 31, 2007 (HealthDay News) -- Smoking just one marijuana joint is the same as smoking five cigarettes in terms of the damage it does to your lungs, a new study found.
Lung damage from marijuana results in chronic bronchitis and other respiratory problems. But whether marijuana causes emphysema or lung cancer isn't clear, the researchers said.
"This damage is a full range from symptoms to structural lung damage and reduced lung function," said lead researcher Dr. Richard Beasley, director of the Medical Research Institute of New Zealand, in Wellington.
Beasley thinks marijuana smokers should heed the study's findings. "Many people think that marijuana is safe, but this shows that it's not safe. Hopefully, this will avoid a lack of knowledge among smokers," he said.
For the study, Beasley's group collected data on 339 people. The group consisted of people who smoked at least one marijuana cigarette a day for five years; people who smoked a pack of tobacco cigarettes a day for at least a year; and people who smoked both. There were also people who didn't smoke either tobacco or marijuana.
All the study participants had lung X-rays and took breathing tests to see how well their lungs worked, according to the July 31 online report in the journal Thorax.
Among the 75 people who smoked only marijuana or the 91 who smoked tobacco and marijuana, there were complaints of wheezing, coughing, chest tightness and phlegm. But, the researchers found signs of emphysema only among the people who smoked just tobacco or tobacco in combination with marijuana.
Marijuana did, however, damage the lungs and stopped them from working properly. The drug decreased the number of small fine airways, which carry oxygen and waste products to and from the blood vessels. In addition, marijuana damaged the large airways, blocking airflow and making the lungs work harder, the researchers found.
The amount of damage was directly related to the number of joints smoked, with more marijuana associated with more lung damage, Beasley noted.
The extensive damage from marijuana results from its higher burn temperature, and because it is inhaled more deeply and held in the lungs longer than cigarettes, Beasley explained. "In addition, there is no filter," he said.
One expert thinks this study is the first to really explain the risks to the lungs posed by marijuana.
"We have always suspected that marijuana causes lung damage, but it's nice to have it quantified," said Dr. Norman Edelman, chief medical officer at the American Lung Association. "Now we can say much more strongly, to people who smoke marijuana, that they are doing bad things to their lungs."
There are still many unanswered questions about marijuana smoking, Edelman said. "Do marijuana smokers go on to get chronic obstructive pulmonary disease?" he asked. "We don't know that."
For more about marijuana, visit the U.S. National Institute on Drug Abuse.