Doctors have warned of the dangers of methadone, a heroin substitute used to treat addicts, after three deaths at one south London hospital this year, writes Elaine Fogg.

Yesterday doctors at King's College Hospital said examples of the class A drug are being taken at raves in huge doses for a quick high. If it is mixed with alcohol the effects can be fatal.

The pain killing synthetic drug is given to registered heroin addicts but doctors are worried that dealers are getting supplies. Addicts are usually prescribed 10mg-20mg, but it can take several hours for the drug to take effect. Ravers seeking an instant high are taking up to 50mg.

Robert Ware, a senior consultant for King's College intensive care unit, said: 'Clubs are getting supplies of methadone in 100mg or 200mg doses. If you take this drug it doesn't have an immediate effect so people are taking it in large quantities.

'We have had three deaths from overdoses this year, but I see only the tip of the iceberg.