The harm principle is the bolded phrase quoted: "That the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others."
A corollary to harm to others is regarding harm to self: "Over himself, over his own body and mind, the individual is sovereign."
The Harm Principle
So we must see if the use of marijuana, for medical or recreation use violates the Harm Principle. There is nothing in the smoking of marijuana which causes harm to others. Actions taken while under the influence may cause harm but that is the fault of those actions taken irresponsibly, like driving, and it is not the fault of the use of marijuana. A corollary is alcohol and cigarettes.
There are several areas we can look at to see if smoking Marijuana may violate the Harm Principle. These areas are Violence, Operating vehicles while intoxicated, and Second hand smoke.
Violence
Marijuana smokers do not exhibit increased violent tendencies. This is in contrast to alcohol which lowers inhibitions and may lead to increased violence. This is not an issue for marijuana.
Operating vehicles while intoxicated
As mentioned above, operating a vehicle while intoxicated is not harmful because marijuana was taken, but because poor judgement was used and the decision to operate a vehicle was made. It is the operation of a vehicle while in a state of intoxication that is harmful, potential or actual, and not merely the intoxication. This is the same as alcohol. The argument is made that the intoxication causes the poor judgement that leads to the operation of a vehicle, but this is again not the fault of being intoxicated. There are many thousands who make the correct decision when faced with this choice.
Second hand smoke
The volume of marijuana smoking is much less than cigarettes. Where one may smoke 20-30 cigarettes and day, chronic marijuana smokers will smoke 3 or 4 times a day. So in keeping this in perspective, the volume of marijuana smoke is much less.
Smoking indoors, in a non-ventilated room, may produce a contact buzz. Smoking outdoors will disburse the smoke too much to be harmful or cause a contact buzz. Certainly smoking marijuana will follow the same smoking laws that cigarettes follow, which typically means no smoking indoors in public establishments. Often it means no smoking around entrances to businesses or public buildings.
Smokers, in general, should be respectful of non-smokers. However, smokers have the right to smoke and non-smokers need to show some common sense and avoid smokers if they have issues with it. This creates a situation where there is no harm.
There is a difference between smoking being offensive, but not harmful, and it being outright harmful. Second hand smoke is only offensive, especially outdoors.
Result
As shown, there is no violation of the Harm Principle. Under what principle, then, we may ask, is Marijuana to be considered criminal? The answer is none.
So, what can we do about it?
The classification of marijuana as a Schedule 1 Narcotic should be overturned immediately. Marijuana should not be classified on any Schedule. It should be classified as Alcohol is, regulated but not a Controlled substance.
All criminal code regarding marijuana should be revised.
The standards for security clearances should be immediately revised to exclude any mention of marijuana as a substance investigated under drug use.
The DEA should be forced to stop pursuing marijuana crimes, including the production, transport, distribution, sale and consumption of marijuana.
Regulation should be put into place for the production, transport, distribution and sale of marijuana.
Release all non-violent drug offenders involved in marijuana from prison.
All drug eradication programs with foreign governments, relating to marijuana, should be stopped.
These actions are to be taken under the firm principle that Marijuana use is not a violation of the Harm Principle. Another colloquial way to say this is the phrase "No Harm, No Foul".
Pay no attention to this drug addicted troll.