The situation Rai is a bit more complicated . The oil for sale in holland and Barrett and on line is a component is cannabis called cpd. This is legal. The controversy in the press concerns the oil containing cpd and th c. Thc is the part which gives you the high and is hallucigenic hence illegal. What this means for medical use for dystonia I am not sure. It is this latter preparation that could more effective than cpd alone. An online search might tell you, but I found it did not give a dose for dystonia
Tim