The latest research says the effects of a single cannabis 'joint' could damage the lungs as much as smoking up to five tobacco cigarettes one after another.
The scientists say the effects of cannabis is made worse by how the joints are smoked and that the drug is capable of damaging the large airways in the lungs causing symptoms such as coughing and wheezing.
The New Zealand scientists say cannabis also damages the ability of the lungs to get oxygen and remove waste products from tissues.
Experts say the research confirms suspicions that the drug represents a serious health risk to the lungs, and that smoking a joint can be more harmful to the lungs than smoking a cigarette.
For the study researchers from the Medical Research Institute of New Zealand, Wakefield Hospital and the Wellington School of Medicine and Health Sciences, studied 339 volunteers up to the age of 70.
By taking CT scans of their lungs and testing their lung function through breathing tests they were able to assess their lung damage.
The 339 participants were divided into four groups: - cannabis smokers, combined cannabis and tobacco smokers, tobacco smokers, and non-smokers.
All were given a questionnaire on their smoking habits.
Seventy five people smoked only cannabis, and 91 smoked both; eighty one people did not smoke either, and 92 smoked only tobacco.
Cannabis smokers were included if they had smoked at least one joint per day for at least five years, while tobacco smokers had to have smoked 20 cigarettes per day for one year.
The tests revealed that one joint could cause as much damage as up to five cigarettes and also reduced the numbers of small, fine airways that transport oxygen and waste products to and from blood vessels in the lungs.
Cannabis smokers reported symptoms such as wheezing, coughing, chest tightness and excessive phlegm production.
Cannabis also damaged the function of the large airways of the lungs, obstructing air flow and forcing the lungs to work harder, contributing to symptoms such as coughing, and the development of bronchitis.
The researchers say the extent of the large airway damage was directly related to the number of joints smoked and the more joints smoked, the more damage was evident.
Cannabis smokers were however not found to suffer from emphysema, a serious and crippling lung disease which was previously thought to be linked to the drug.
The team say the impact of cannabis was possibly due to the way in which cannabis joints are smoked, as joints do not usually have filters, and they reach higher temperatures with users inhaling more deeply and holding their breath for longer than cigarette smokers.
The revelations follow other recent research which has linked cannabis to a 40% higher risk of psychotic illnesses such as schizophrenia among users.
The research is published in the journal Thorax.