Dr. Declan Bedford:

Cocaine is faster acting and would be out of the system quicker. The point is the blood tests can tell the metabolites of the cannabis. Some are fast and disappear quickly. It is not just the cannabis but the chemical constituents of it and they tell whether it has been more recent. It is also the case that cannabis has a long-term effect on people. People think it is a harmless drug. It is far from harmless and it has a long-term effect.