Cannabis is reported to be effective for the relief of intractable pain.

  

However, the neural bases for pain relief are debatable. This study examined the effect of the delta-9-tetrahydrocannabinol (THC) on induced hyperalgesia. First, subjects rated the intensity (degree of burning and sharp sensation) and unpleasantness (how much the sensation bothered the subject) of ongoing pain before and after receiving THC. Second, subjects underwent an fMRI to identify where THC affected brain activity that was associated with induced hyperalgesia.

Hypothesis: THC effects on the affective qualities of pain are linked to the activity in the amygdala. Main findings were:
-THC significantly reduced pain perceived unpleasantness, but did not have a significant effect on perceived pain intensity.
-On fMRI, THC increased amygdala activity (analgesic effect) and reduced the activity between the amygdala and the primary sensorimotor cortex.
-This reduction in amygdala-sensorimotor cortex function connection was linked to the reduction in unpleasantness of pain.

This data reveal that specific effects of THC analgesic effects in reported healthy volunteers. Identifying patients who rely on similar central effects from cannabis-based medicines for pain relief remains challenging. > From Lee et al.; Pain 154 (2013) 124–134. All rights reserved to Elsevier Ltd.