Abusers of synthetic drugs may not always carry clear tell-tale signs.
It is almost impossible to tell, said a former drug enforcement officer.
The man, who spoke on condition of anonymity, said the profile of those who abuse drugs like methamphetamine (Ice), or Ecstasy, is different from that of hardcore users of heroin or opium.
"Abusers of synthetic drugs can be professionals, the rich or those who look like gym rats," said the man in his 60s with 30 years of drug enforcement experience.
"That's why I don't blame the parents of the people who overdosed at the music festival in Kuala Lumpur. If I can't tell, how do you expect them to know?"
On Sunday, The New Paper reported that the last day of the Future Music Festival Asia in KL was cancelled after six Malaysian concertgoers had collapsed at the festival grounds at Bukit Jalil National Stadium on Friday and later died from an apparent overdose of Ice.
An estimated 85,000 people had to miss Saturday night's performances from Grammy winners Pharrell Williams and Macklemore & Ryan Lewis on the last day of the three-day music festival.
At least four Singaporeans were also reported to have been hospitalised for suspected drug overdose.
The latest from Bernama news agency said that of the 29 people arrested, nine were believed to be Singaporeans. For the 14 concertgoers who were hospitalised, all were reported to be in a stable condition, a police spokesman told Bernama.