'Legal high' ambulance callouts double in London
The number of people needing help from paramedics after taking so-called legal highs has more than doubled each year since 2013.
London Ambulance Service (LAS) attended 50 callouts in the financial year 2013-14. This rose to 129 in 2014-15 and 271 in 2015-16.
The sale of psychoactive substances such as Spice was banned in May.
Last year they were linked to more than 100 deaths in the UK and attributed to a rise in violent assaults in prison.
The ambulance service figures obtained as part of a BBC Freedom of Information Act request showed nine people needed hospital treatment in 2011-12.
This rose to 178 in 2015-16. Between April and June this year there has been 69 incidents, with 38 needing hospital treatment.
The Angelus Foundation - which warns people of the dangers of psychoactive substances - described it as an "escalating problem".
A spokesman said homeless people and prisoners were more likely to be affected by using drugs such as Spice, which is a synthetic cannabis.
"There [is] a switch amongst homeless people from substances like heroin and crack and alcohol to Spice because it's cheaper and more potent," he said.
The YMCA charity warned before the Psychoactive Substances Act was passed that two-thirds of young people who used the drugs were likely to continue using them.
Chief Executive Denise Hatton said it was clear the harms associated with legal highs were growing and called for the ban to be "supplemented with impartial information and advice, along with specialist support".
Neil Thomson, deputy medical director at LAS said the use of "legal highs" was an issue for paramedics.
"Substance misuse can pose a big problem for our service especially at large public events where we treat many people who present symptoms having taken these types of drugs," he added.