The heart rate is elevated so people with problems like angina should be careful. Reproductive hormones seem to be suppressed. The immune function is suppressed but this has not given rise to problems with Aids patients. Withdrawal symptoms are mild and flu-like. There is no evidence for developing a craving.
Exceptions are people who use cannabis as a crutch.
People who take it for its mood altering qualities should avoid it. When smoked cannabis is carcinogenic but not if eaten or taken as tea. Minor symptoms such as dizziness, sedation, dry mouth, blurred vision and mental clouding have all been reported. Practically every centrally acting drug has commonly got these side effects. If a trial goes ahead it would be MS specific, probably looking in particular at its therapeutic effects on pain, particularly in spasticity.