The GPR 55 is a receptor found to react to both THC and CBD, this has led to some scientists suggesting that it should be reclassified as CB3. There is some evidence that it plays an important role in the regulation of bone metabolism, as well as improving inflammatory pain control and on tumour cells proliferation. However the lack of selective GPR55 agonists and antagonists makes further research difficult at this stage.
Pharmaceutical companies initially hoped chemicals acting on GPR 55 would reduce blood pressure, however rats bred to not have GPR 55 had no issues with blood pressure so drug development has stopped.
CBD is primarily an antagonist of GPR55 and stops its expression, leading to some of its physiological effects. It is poorly understood however, with its role in several areas of the body poorly understood.