Police have issued a warning about ecstasy pills after a woman died and two men were taken to hospital after taking the drugs.
All three were Vietnamese nationals in south London, leading Scotland Yard to direct the advice towards the south-east Asian community.
The pills are orange and rectangular, with no distinctive markings on them.
The 22-year-old woman died in King's College Hospital on August 28 after being taken ill at a house in Knight's Hill, West Norwood. Her family has been informed and a post mortem examination will be carried out on Monday.
One of her friends, a man in his 20s, was also taken to hospital in a critical condition and has since been discharged.
They are both believed to have taken ecstasy with other friends at Crystals nightclub in Lewisham, police said.
Analysis of pills seized from the address in Knight's Hill found that they contained MDMA (ecstasy) and ketamine, according to officers.
A 17-year-old boy was taken ill at the Electric nightclub in Brixton on September 3.
He is also believed to have taken the same drug and is in a critical condition in hospital.
Police suspect several other people became ill at the Electric having taken what they believed to be ecstasy, but left the venue without calling emergency services.
A Met spokesman said: "Anyone who has taken these substances and feels unwell is advised to seek medical treatment.
"There is always a risk that people may suffer ill-effects through taking illegal drugs, and the clear advice of police and medical professionals is not to take such substances."
Anyone with information can call Lambeth CID via 101 or Crimestoppers anonymously on 0800 555 111.