Black people are more likely than white people to be charged with possessing cannabis, a police study has found.
The survey follows the declassification of cannabis
According to the research by the Metropolitan Police, 25,000 people in total were accused of possessing the drug between January and April 2006.
Scotland Yard said further work was needed to understand why more black people were charged.
But critics said it was because young black people were being unfairly targeted under stop-and-search powers.
The survey was carried out to examine how offences relating to the possession of cannabis had been enforced since it was downgraded to a Class C drug in 2004.
Figures showed that of those arrested, 40% were African and Caribbean, 28% were white Europeans and 13% Indian and Pakistani.
Of those who were later charged, 18.5% were African or Caribbean and 14% were White Europeans.
Nineteen per cent of white Europeans were given a caution, rather than being taken to court, compared with 14% of people from African or Caribbean communities
A Scotland Yard spokeswoman said: "We recognise there is disproportionality within the wider criminal justice system and there are complex reasons for this.
"We are undertaking further research of these figures in order to understand what the reason for the over-representation is."
Stop and search
Paul Cavadino of crime reduction charity Nacro said: "Home Office research has found that... young black people are no more involved in drug use than young white people."
He put the disproportionate number of black people caught and charged for carrying drugs down to the "racially skewed use of stop and search powers".
And one of the Met's senior ethnic minority officers said young black men were being unfairly targeted by the authorities.
Ch Supt Ali Dizaei said drug users are known to be predominantly white, middle class men.
"But it is black men who are disproportionately being stopped and searched and being locked up," he said.