The holes in Samantha Wilson's lungs are getting bigger.
Smoking cannabis can cause severe lung damage
There is no cure for her illness and if it continues to get worse it will eventually kill her.
Samantha is 37 and has emphysema, a progressive condition normally associated with older people who have smoked tobacco regularly throughout their lives.
Samantha's doctor, Dr Onn Min Kon, a consultant physician of respiratory medicine at St Mary's Hospital in London, believes her cannabis smoking may be to blame for her condition.
Dr Kon said he had several other young patients who smoke cannabis and have lung diseases normally seen only in older tobacco smokers.
He said: "I've got a collection of young people who have lungs that look like they're 65-year-olds."
Such case studies have prompted Dr Kon to plan a study comparing the lungs of patients who smoke cannabis with those who smoke only tobacco.
When Samantha, of Maida Vale, London, was diagnosed with emphysema at the age of 34 she had been smoking cannabis for 20 years.
She had begun by smoking two joints a day, but was eventually smoking up to 10 a day.
According to the latest figures from charity Action on Smoking and Health, the average tobacco smoker smokes between 13 and 14 cigarettes every day.
Samantha believes she is living proof of the effects cannabis can have on lungs.
She said: "If I don't stop smoking I won't be around much longer - there is no cure for emphysema, the holes in my lungs are getting bigger.
"There should be adverts showing people like me."
Dr Kon uses images of his patients' lungs to assess damage
When smoked, cannabis produces many of the same chemicals as a tobacco cigarette, but may damage the airways to a greater extent.
In a 2002 report, the British Lung Foundation estimated that three to four cannabis cigarettes a day were associated with the same amount of damage to the lungs as 20 or more tobacco cigarettes a day.
So far though, it has been difficult to separate the effects of cannabis smoking from those of tobacco smoking in patients, as many users smoke both.
In his study, Dr Kon will use lung function tests and CT scan pictures to look for lung damage.
Such a study using CT scans has not been done before and Dr Kon said even people with apparently normal lung function could have problems, such as holes in their lungs, which would show up on these scans.
He said these people may have no symptoms but could still have respiratory diseases.
Emphysema is a normal feature of ageing
The alveoli, or small lung cells, become damaged
The condition develops progressively, causing "holes" in the lungs
The lungs lose their elasticity and breathing is difficult
Smoking accelerates the ageing process in lungs
In some people the damage becomes noticeable in their lifetime
Previously the link between emphysema and cannabis smoking has been difficult to prove, and the risks are often overlooked by people, who are generally concerned only about lung cancer.
Samantha said: "I'd never even heard of emphysema when I was diagnosed, and I don't think people know there is a risk of getting it."
The British Lung Foundation also called for more awareness of the issue.
A spokesperson said: "Research carried out by the British Lung Foundation found that smoking cannabis alone can cause severe lung damage.
"It is vital that people are fully aware of the dangers so they can make an educated choice and know the risks fully."