Of the thousands of people who attended Sunday's festival, 128 used the drug-checking service offered for free by the STA-Safe consortium.

Volunteers tested 85 samples, half of which contained substances such as lactose, paint, toothpaste and condensed milk.

Canberra emergency physician and consortium member Dr David Caldicott said the infrared spectrophotometer used to test the drugs was so sophisticated, it was even able to pick up the kind of condensed milk used.

And while many of the pills tested were "duds", Dr Caldicott said many were potentially quite harmful.

"The overwhelming majority of psychoactive substances we analysed were MDMA or as you might know it, ecstasy and in some cases it appeared to us that was of quite considerable purity," Dr Caldicott said.

"I think many of patrons initially thought that a product that contained MDMA of high purity was a success and of course we were able to disabuse them of that because of course the purer an MDMA product is, the more likely you are to overdose on it."

The consortium red-flagged two substances, one — n-ethylpentylone, a stimulant responsible for the hospitalisation of 13 people in New Zealand last month — forced Dr Caldicott to make a late-night phone call to the ACT's Chief Health Officer.

"It’s something that causes me fear and there’s not a lot that does," Dr Caldicott said.

The other substance is believed to be NBOMe, a powerful hallucinogen linked to three deaths in Melbourne in 2017.

Ambulance commander Toby Keen said two people had been taken to hospital due to acute intoxication, either from drugs or alcohol.

On-site paramedics and first aid staff treated another 86, largely due to intoxication as well.

Pill-testers were able to provide paramedics with information about what was circulating the festival almost immediately, so they could treat people accordingly.

Critically, none of the people who presented for treatment had a wristband that indicated they had participated in the pill-testing trial.

"Overall we'd say most of the people presenting to us were intoxicated in some form, it’s very difficult for us to work out in the field whether that’s alcohol drugs or a combination of the two but I suspect the vast majority of that is alcohol," Mr Keen said.

"We didn’t see anyone who'd been to pill-testing. It's worthwhile noting the people we transported for acute intoxication hadn't been to pill-testing which I think is actually a good success marker for the pill-testing."

Mr Keen also said the number of people treated for intoxication was similar to previous years, scotching claims the trial would encourage higher levels of drug-taking.

While ACT Policing did not target people entering the health tent where the pill-testing was taking place, Chief Police Officer Justine Saunders said two people were arrested for drug-related crimes.

One of the people arrested was found with 18 pills. The other was arrested for possession of an MDMA tablet and was directed into a drugs diversion program.

Chief Police Officer Saunders said neither of the people arrested on drugs offences had interacted with the pill-testing service.

She said while there was no exclusion zone around the tent, police kept away.

"Our intention was to focus our efforts on those who were trafficking and selling drugs, focusing on the criminality of drugs but allowing the pill testing to occur in a safe way," Chief Police Officer Saunders said.

Five others were taken into custody during the festival for anti-social behaviour and intoxication.

ACT Health Minister Meegan Fitzharris said the trial was a success, and had shown there was a demand for the service.

ACT Greens leader Shane Rattenbury praised it as a milestone for Australian drug law reform.

ACT Chief Health Officer Dr Paul Kelly said the government and the consortium would evaluate the results of the trial to determine whether pill testing would become a regular fixture at ACT music festivals.

He said while abstaining from illicit drug use was safest, authorities needed to be willing to explore new ways of reducing drug-related harm.

"If we continue to do what we’ve been doing for the last 20 or 30 years in relation to drug policy we will continue to get the issues we face at festivals and other places every weekend, day in and day out in Australia," Dr Kelly said.

"At least with pill testing they have some information to guide their behaviour and we could see yesterday people changing their behavioural choices on the basis of that information that they were given."

However ACT Opposition legal affairs spokesman Jeremy Hanson was not convinced the trial had reduced drug-related harm at the festival.

"All we know is on the weekend many people got sick from taking drugs," Mr Hanson said.

"Obviously what’s happened is many hundreds of people have been given the message that it’s a legal free-for-all to take drugs and the drugs they take are safe, particularly if they get them tested, when that’s not the case."