Thousands of patients are to be given cannabis in the first large-scale study of the drug's clinical effect.
Medical cannabis, which is grown to a precise grade of active ingredient, was legalised in the UK a year ago.
But only a handful of patients have since been prescribed the drug on the NHS because of what medical authorities have called a "paucity of evidence" that it works and is safe.
The only option for patients is to either source cannabis illegally, and risk prosecution, or pay for a private prescription of the drug
The new study, called Project Twenty21, will subsidise cannabis for 20,000 patients to test its impact on seven conditions: chronic pain, multiple sclerosis, epilepsy, post-traumatic stress disorder, Tourette's syndrome, anxiety disorder and substance abuse.
Professor David Nutt of the organisation Drug Science, which is running the study, told Sky News: "I believe cannabis is going to be the most important innovation in medicine for the rest of my life.
"Cannabis medicines can be life-saving in disorders like severe childhood epilepsy.
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"There are children who have died in this country in the last couple of years because they haven't had access to cannabis.
"It's outrageous, it's unnecessary and we want to rectify it."
Lucy Stafford used to suffer severe chronic pain from the genetic connective tissue disorder Ehlers Danlos syndrome, which meant she could dislocated her joints simply by rolling over in bed. She was treated with opioid drugs, but they had little effect and had serious side effects.
Since paying privately for medical cannabis, at a cost of £800 a month, her pain has reduced so much that she has stopped other treatments and started university.
She told Sky News: "Now I can get up in in the morning and even if I'm in the most unbearable amount of pain and feel like passing out and being sick I can take my medication and be able to function and focus and live my life.
"If other medications were effective for us we wouldn't need this.
"But the whole point is that everything that is currently being offered, such as opiates, diazepam and other horrible medications, just do not manage the conditions that we are living with.
"Medical cannabis does.&qRead More – Source