Smoking cannabis damages the immune system.

Cannabis damages the immune system, leaving the body open to diseases from pneumonia to cancer, research suggests.  In experiments, THC, the chemical behind the ‘high’ of cannabis fuelled the production of a flood of cells thought to weaken the body’s inbuilt defences.


The finding suggests that cannabis, the drug of choice for many Britons,  increases vulnerability to breast, bladder, lung and other tumours, as well as bacterial infections such as Legionnaires disease.

Worryingly, skunk, the super-strength cannabis that is particularly popular, may be extra-damaging, due to its extra-high THC content.

While cannabis’s links to devastating mental health problems are well known, its potential to wreck the immune system has received less attention.

The American research focused on the effect of cannabis chemicals including THC on the immune system.

In tests on mice, they triggered the production of a ‘massive’ number of immune cells called myeloid-derived suppressor cells or MDSCs.

These normally act as a safety brake on the immune system stopping its battle against disease from spiralling out of control.

But in the case of cancer, they may actually make it easier for tumours to grow, the European Journal of Immunology reports.

Lead researcher Dr Prakash Nagarkatti, from the University of South Carolina, said: ‘These results raise interesting questions on whether increased susceptibility to certain types of cancers or infections caused from smoking marijuana results from induction of MDSCs.

‘MDSCs seem to be unique and important cells that may be triggered by inappropriate production of certain growth factors by cancer cells or other chemical agents such as cannabinoids, which lead to a suppression of the immune system’s response.’

In large quantities the cells may also leave the body open to infection with germs such as those that cause pneumonia.

The findings could have important implications, not only for those who use the drug recreationally but for those taking it to improve their health.

The drug is used to ease the symptoms of multiple sclerosis and THC can be used in treatment of cancer, glaucoma and HIV.

On a more positive note, a greater understanding of how to weaken the immune response could lead to new treatments for diseases caused by the immune system turning on the body.

Multiple sclerosis and rheumatoid arthritis are among the conditions caused by such ‘friendly fire’.

Dr Nargarkatti said: ‘Marijuana cannabinoids present us with a double edged sword. 

‘On one hand, due to their immunosuppressive nature, they can cause increased susceptibility to cancer and infections. 

‘However, further research of these compounds could provide opportunities to treat a large number of clinical disorders where suppressing the immune response is actually beneficial.’ 

The mental health risks associated with the drug are well documented.

Those who smoke cannabis regularly at 18 are 1.6 times more likely to suffer serious psychiatric problems, including schizophrenia, by their mid-20s. 

For those who are regular users at 15, the stakes are even higher, with their risk of mental illness by the age of 26 being 4.5 times greater than normal.

Latest figures show that cannabis ruins at least 12 young lives every day.

Some 4,400 youngsters needed treatment for serious problems last year after smoking the drug.

They were referred for treatment by psychiatric services or families worried that the youth’s life was falling apart, according to the NHS.

Henry Scowcroft, of Cancer Research UK, said it was impossible to tell if the effects seen in mice would extend to people.

He added: ‘The issue of whether cannabis can cause cancer is a controversial one that is still not settled. What is certain is that most UK cannabis users smoke the drug with tobacco, which is still the single most important cause of cancer.’

Via Daily Mail