Police guidelines on how to deal with cannabis users are set to change following the decision to reclassify the substance as a class B drug. BBC News explains the rules.
How are drugs classified?
Since the 1970s, the law has placed drugs in three categories based on scientific evidence of the harm they can cause.
Class A is the most harmful, including things like heroin and morphine; class B is the middle group, covering amphetamines and barbiturates; and class C includes those judged to be the least harmful, such as anabolic steroids.
Where does cannabis sit?
Cannabis is to be returned to class B status.
It had previously been classified in this way but, in January 2004, the drug was downgraded to class C by the then Home Secretary David Blunkett based on the advice then available.
In practice this meant there would be a "presumption against arrest" when officers come across someone with cannabis in their possession.
When cannabis was previously classified as class B, police were expected to arrest users - however the reality was often quite different. Many officers were taking what they would describe as a pragmatic response - confiscating the drug, giving a caution on the street and leaving it at that.
So what did the previous reclassification mean for cannabis users?
Most people found in possession of cannabis found they were unlikely to be arrested. Instead, police gave more informal on-the-spot warnings.
Could the police still arrest people over cannabis?
Yes. Police still had that power, though they were advised to use their discretion.
Persistent cannabis offenders have always been more at risk of arrest and police also focused on drug use in situations where there is the potential for trouble.
The law regarding dealing the drug remained unchanged - a maximum of 14 years in prison.
Why were the 2004 changes brought in?
The Home Office and the police hoped the changes would mean officers would spend less time arresting and processing cannabis offenders and more time focusing on more harmful drugs like heroin, cocaine and crack.
Why has the home secretary has decided to change the classification back again?
Jacqui Smith said she wanted to reverse Tony Blair's 2004 downgrading of the drug to class C because of the "increased strength" of cannabis. The home secretary highlighted "uncertainty at the least" on the future impact on young people's mental health as a result of using the drug.
The decision came despite the Advisory Council on the Misuse of Drugs' review which concluded that the drug should remain a class C substance.
Earlier this year, Gordon Brown indicated that he wanted cannabis back at class B - saying that class C had sent the wrong signal. At the time of the 2004 classification, ministers pledged a tough public education policy.
Critics of the government's shift say that rather than criminalising users they should invest in that public health programme to make drug use unacceptable.
What about the mental health debate?
Opinion is divided on cannabis and mental health. However the type of cannabis available has itself changed considerable. Skunk, one type available on the street, is far stronger than previous varieties.
So is there confusion among the public?
The reality is that there is a generation gap. The young and many people under 35 would probably have a completely different attitude towards cannabis use than senior politicians or police chiefs because of its ubiquity in higher education and the UK's clubbing scene.