The highly addictive drug crystal meth is moving away from clubs and becoming more widely available on London's streets, a drugs court judge reveals.
Defendants are testing positive for the drug, says the judge.
District Judge Justin Phillips sits in west London at one of two drugs courts set up in a pilot scheme by ministers.
The scheme, designed to prevent low-level offenders committing further crimes, has been running for a year.
Judge Phillips said crystal meth was cheap, caused a lot of violence and was "probably the most addictive drug".
"It is very cheap, you can get it not far from here for £20.
"That gives a four to five-hour high but the comedown is frightening, with symptoms including paranoia, stroke, heart problems, irritability and self-harm. It can lead to a lot of violence."
Crystal meth has often been taken by people who come into court, he said.
"I know it's being taken, because everyone on a drug order is tested, said District Judge Phillips.
"A lot of them don't know they are taking it - cocaine is cut with it, skunk is being cut with it, which may be in an attempt to hook people, as it is so addictive."
The drug was re-classified as Class A last month in a bid to prevent it taking off.
People who use the stimulant will face up to seven years in jail and an unlimited fine, while dealers could get life behind bars.