Medicines by law, have to be pure substances, single chemicals, so that their actions are predictable and controllable. Cannabis contains around 400 chemicals. Some of the 60 or so purified cannabinoids (substances unique to the cannabis plant) have been extracted and are being tested as potential medicines - that is correct procedure. No-one would suggest you eat mould (Penicillium) on bread to get your penicillin.
Synthetic purified THC, Nabilone, (Marinol in USA) is already available on hospital prescription to stimulate the appetite in AIDS patients and combat nausea, but has many side-effects and is not popular among doctors. A combination of THC & CBD is licensed in the UK as Sativex. In October 2014 it was rejected as non-cost effective by NICE.
The modest benefits and high cost of Sativex did not justify it's use
I have been apologising to the American people for the last 10 years for promoting the decriminalisation of cannabis. I made a mistake. Marijuana combines the worst effects of alcohol and tobacco and has other ill effects that neither of these two have
Dr Robert Dupont, founder of NIDA (National Institute for Drug Abuse)
It all started in 1979 when an American pot smoking lawyer said, "We will use the medical marijuana argument as a red herring on the road to full legalisation". His successor at NORML (National Organisation for the Reform of the Marijuana Laws), said, “Medical marijuana is our strongest suit. It is our point of leverage which will move us towards the legalisation of marijuana for personal use”.
Many pro-legalisers are users, or their children are. Others are libertarians who think we should be able to do what we like with our bodies. That’s fine as long as it doesn’t interfere with anyone else. But it always does.
Stoned drivers can and do kill other people. Addicts and the mentally-ill need treatment at the taxpayers expense. Stoned workers are inefficient and unproductive and may not care properly for their children. Magistrates are warning that children are stealing mobile phones to get money to buy the drug. And passive smoking does occur. A non-user at a pot smoke-laden party drove home and had no recollection of doing it.