People with MS who smoke pot say it helps with symptoms such as pain, but does that come at the expense of a clear head? A small preliminary study hints that people with multiple sclerosis who smoke marijuana may process thoughts more slowly than people with MS who do not.
If true, this could be problematic for MS sufferers – some 40% of whom already suffer cognitive dysfunction as part of their disease. Typically, MS patients can have slower reaction times and poorer working memory.
Omar Ghaffar and Anthony Feinstein at Sunnybrook Health Sciences Centre in Toronto, Canada, wanted to find out if smoking pot made things worse for MS patients and affected their mental health.
Pot-smoking in healthy people has been linked to psychosis, delusion, depression and anxiety, and MS patients report higher levels of anxiety and depression than the general public even without the drug.
The researchers recruited 140 patients with MS, 10 of whom said they were regular users of pot. All 10 had smoked at least once in the past month and gave various reasons for smoking, including "for spasticity and bladder symptoms" and "for the high".
The researchers tried to match each pot-smoker with four control members who were similar in age, education and disease progression.
Ghaffar and Feinstein administered several tests to measure aspects such as anxiety and depression, suicidal feelings and social support. They also assessed cognition, using a specialised test for MS patients, and a computerised version of a test that measured how quickly and accurately they recalled associations between symbols and numbers.
The researchers found that pot-smokers were more likely to have psychiatric issues overall such as anxiety or depression, but no more likely to have a diagnosis for a specific mental illness than those with MS who did not smoke marijuana. Nor did they fare worse on the cognitive test. They were, however, significantly slower on the symbol-digit matching test.
The study is preliminary, stresses Feinstein, but he believes it suggests the effects of cannabis on MS patients should be studied more carefully. "You've got a group that's cognitively impaired," he says, "and along comes cannabis which is like a second hit."
But Mark Ware, who studies pain control, at McGill University in Montreal points out just how few adverse effects of cannabis the study found. And even then, causality was unclear. Uncontrolled pain can also affect cognition, he notes.
Still, he is worried that neurologists and patients will be scared off by negative headlines. "Let's not throw out what could still be a useful treatment," he says.
In Canada, patients with MS can legally use cannabis for medical reasons.
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