Yes, of course they can. I think, though, the question is, what the therapeutic benefit of prescribing cannabis is versus its risks. If cannabis is prescribed, the risks of opiates and benzodiazepines are not going to go down. It's not an either-or thing. Opiates and benzodiazepines have terrible problems, but there is far greater evidence of effectiveness, so I don't think that smoked marijuana is a legitimate medicine except in extremely specialized circumstances, such as patients with severe neuropathic pain.
On May 1st, 2014. See this statement in context.