There was a good bit on the BBC morning show (ex news), about 8.45 11th Oct with 2 doctors of different opinions.
Doc A was one involved in Cannabis trials for MS relief
1 - We do not use cannabis itself; only tablets containing a number if its active components.
2 - Smoked cannabis has more tar than tobacco.
3 - there are measurable reaction time penalties 2 days after smoking cannabis.
Doc B was a GP used as 'resident expert'
1 - I see no patients with lung diseases who only smoke cannabis.
2 - I also see patients with alcohol related problems.
3 - Apart from a few psycoses I see no patients with cannabis related problems.
Unfortunately item was too short for too many more arguments.
Given known severe health problems linked with tobacco, if it was discovered today would it be legalised??