Most cannabis users caught by police will in future escape with a warning and confiscation of the drug.
Under new police guidelines, cannabis users will only be arrested in certain aggravating circumstances.
These could include smoking in public, having the drug around children or for being persistent offenders.
But critics say the new rules will cause widespread confusion, with many mistakenly thinking the drug has been made legal.
And mental health campaigners were concerned they would send out the message that cannabis was risk-free.
The guidance does not specify an amount users can claim is for their own consumption.
But anyone under 17 found using cannabis will still be arrested, under the guidelines drawn up by the Association of Chief Police Officers (Acpo).
Officers dealing with cannabis possession will still be required to record the incident as a crime.
And users will still be arrested in areas where local residents have complained.