A security firm is investigating allegations that one of its guards took drugs during their shift at Sydney's Stereosonic music festival where a woman collapsed before later dying of a suspected drug overdose.

The investigation comes after Stereosonic's emergency medicine contractor forbid staff from talking to police, who are preparing a brief for the coroner.

Festival organiser Totem Onelove said on Tuesday it had told all festival staff that only "the heads of each organisation" were allowed to answer police questions. It said each contractor had co-operated fully with police.

Media outlets reported a security guard had been partying during his Saturday shift, high on the drug GBH, before he was taken to hospital.

"Reddawn Security takes the allegations very seriously and has launched a full internal investigation regarding the alleged behaviour," managing director Simon Auston said.

"We do not condone any of our staff abandoning their posts or taking illicit substances with patrons either during or after a shift."

Sylvia Choi, 25, died after collapsing at the electronic music festival, which was attended by more than 48,000 people.

Ms Choi, a pharmacist from Oyster Bay in Sydney's south, fell ill about 5.15pm and was pronounced dead less than four hours later. Police refused to comment on speculation she had taken MDMA and ecstasy.

Fairfax Media reported on Monday that Stereosonic's private medical contractor, Event Medical Services, emailed staff saying they were not to reply to police questions.

Event organiser Totem Onelove said all festival staff and contractors were told "any questions from the police or media relating to the incident should only be communicated by the heads of each organisation".

Totem Onelove operations manager Dave Rubin said EMS was a "valued contractor".

"Their execution was faultless, their quick responses saved lives and their efforts were second to none," Mr Rubin said. According to Totem Onelove, one quarter of EMS staff on site were students.

Since Ms Choi's death, harm reduction advocates have renewed calls to allow drug checking services that would tell users the purity and composition of their pills and powders.

"Drug users aren't stupid," Deakin University senior lecturer Matthew Dunn said. "They want to look after their health and they'll make appropriate choices based on the information they have."

Harm Reduction Australia vice-president Tony Trimingham, who lost his son to drugs in the '90s, said the introduction of pill testing could save lives.

"If we look at the tragic death at the weekend – [Sylvia Choi] was a pharmacist, if she had been told, this substance is not what you think it is, I think she would have had enough knowledge not to take it and it's almost certain that death would have been avoided," Mr Trimingham said.

"Festivals are a place where young people gather and use drugs so anything that minimises the damage that drugs do should be applied."

Premier Mike Baird would not be drawn on whether or not he would support the introduction of pill testing at festivals, following their implementation at several large events across Europe.

Opposition health spokesman Walt Secord said there was limited evidence of the effectiveness of drug testing at music festivals.

"As it currently stands, pill testing is a bridge too far and I do not support pill testing kits at festivals," Mr Secord said.

But Independent MP Alex Greenwich and Greens MLC Mehreen Faruqi said the government needed to take a new approach based on harm minimisation.

"Pill testing is a no-brainer, and is done in other countries and is supported by many medical professionals," Mr Greenwich said.

Festival tragedy: five deaths in 12 months

Sylvia Choi, 25

Date of death: November 29, 2015.
Festival attended: Stereosonic, Homebush.
Circumstances: The Oyster Bay pharmacist became seriously ill after taking ecstasy and later died in Concord Hospital.

Date of death: October 25, 2015.
Festival attended: Dragon Dreaming, Yass.
Circumstances: An unidentified Sydney woman died after being found unconscious at 5:30am. Police said they made 78 drug detections at the festival over the course of the weekend.

Date of death: September 19, 2015.
Festival attended: Defqon.1, Penrith.
Circumstances: The former Albury High School student was found unconscious in a tent at the festival. "Our lives changed forever this weekend," his family said in a statement. "We have been deeply affected by this tragedy and we are reeling from the loss."

Date of death: February 7, 2015.
Festival attended: State of Trance, Homebush.
Circumstances: The 19-year-old Kellyville teenager was competing against a friend to see who could swallow the most ecstasy pills. His 20-year-old friend also ended up in a critical condition. "Shocking isn't the word, idiotic is the word," said Police Assistant Commissioner Frank Mennilli at the time. "These people were gambling with their life, it's absolute stupidity."

Date of death: November 8, 2014.
Festival attended: Harbourlife, Sydney.
Circumstances: The former Wenona student died after taking ecstasy supplied by her close friend Rebecca Hannibal, who pleaded guilty to supplying her with drugs she bought from fellow teenager Matthew Forti. In one text message, Ms Bartter said to Ms Hannibal, "I'm not taking three [ecstasy pills] at HarbourLife - I'd die". "And so she did," Judge Graeme Henson said in giving Ms Hannibal a criminal record. Forti was sentenced to at least 12-months jail.