A study from the University of Oxford suggests that cannabis makes pain more bearable rather than actually reducing it. 
In particular, volunteers had a cream rubbed into the skin of one leg to induce pain. They where also given either a 15mg tablet of THC (delta-9-tetrahydrocannabinol) – the ingredient that is responsible for the high when one takes cannabis – or a placebo.
Each participant had four MRI scans which revealed how their brain activity changed when their perception of the pain reduced. Dr Michael Lee, lead study author from Oxford University’s Centre for Functional Magnetic Resonance Imaging of the Brain, said: “We found that with THC, on average people didn’t report any change in the burn, but the pain bothered them less”.
This study shows the great problems of similar research. Subjective opinions can have a major impact on the final result and when human mind is in play, a lot of things run into contradictions. How can the pain be “the same” but at the same time bother you “less”? Wouldn’t that mean that the pain is not the “same”? Or maybe the drug you took increased your ability to withstand pain. But if so, how can you understand that the pain is “the same”?!?
And even more difficult, how can a researcher be objective about these kind of things? How can you rely on someone else’s saying on such difficult to grasp matters and really think you can be “objective”?!?
Perception is a weird thing.
It is what constitutes “reality” for each and every one of us.
Reality is a weird thing.