People suffering from extreme pain as a result of their disease are being given versions of the drugs, which have pain-killing properties.
Academics at Edinburgh University are now leading two clinical trials at the Beatson cancer centre in Glasgow to test the effectiveness of cannabis mouth spray and ketamine, a common horse tranquilliser.
Research shows that pain is uncontrolled in around 20 per cent of patients with advanced cancer who are prescribed morphine-based treatments, and many others experience negative side-effects from traditional painkillers.
But no effective alternatives have been approved for cancer patients on the NHS.
It is hoped cancer sufferers taking part in the new trials will see major improvements in their quality of life, leading the way to the drugs being rolled out nationally.
A spokesman for NHS Greater Glasgow and Clyde said: "We can confirm that two clinical trials are taking place studying the use of cannabinoids and ketamine for pain relief in cancer patients."
Each patient is expected to take part in the trial for approximately six months and results are expected next year.
The cannabis spray, Sativex, is already being prescribed for multiple sclerosis patients.
It works by stopping nerve signals being sent to the brain from the site of pain and was developed so it did not affect the mental state of patients in the way that street cannabis might. It also does not pose the same health risks as smoking the class-B drug.