Andrew Leibie, from Safework Laboratories, says he and other toxicologists - who can't speak out because they work in the public sector - were concerned about a lack of scientific debate.

But pill testing advocates have dismissed his claims, saying their technology was well placed to detect dangerous drugs and prevent deaths.

The ACT government last month gave the green light to a pill testing trial at Spilt Milk festival in November.

The testing will be conducted and funded by a Safety Testing Advisory Service at Festivals and Events consortium and offered for free to festival goers.

Mr Leibie said public statements made by politicians that the trial would help "keep people safe" were potentially misleading because the testing had limitations.

He questioned the reliability of the on-site drug testing, saying he wasn't convinced it would be able to accurately test for potency and detect dangerous new designer drugs.

Mr Leibie said he was also concerned about a lack of reliability if anything less than a whole pill was submitted for testing.

"In the lab we do come across drugs we can't identify in our tests with much more sophisticated equipment," he said.

"We all have concerns about the way the science hasn't been discussed in the media.

"The science of the process has not been debated and it's just been reduced to good versus bad.

"I'm not saying pill testing doesn't have a place but it's been oversold, it's definitely no magic bullet."

He claimed the per capita death rate from new designer drugs was higher in Europe - where pill testing was available in some countries - than in Australia.

But David Caldicott, a Canberra-based emergency medicine specialist who is part of the pill testing trial, said the methodology to be used at the festival was tried and tested across the world.

He said their laboratory grade equipment had the largest possible "library" - gathered from international agencies - which allowed it to identify tens of thousands of drugs, including designer synthetic drugs.

Any drug that could not be identified - for example a newly created designer drug - would show up on the test as an unknown and the consumer would be advised "in the strongest possible terms" not to take the drug.

Dr Calicott said all consumers, regardless of the outcome of the test, would also be told if they "did not want to be harmed by drugs they should not use drugs".

He said analysts who were opposed to pill testing were expecting data that was as foolproof as was needed in a legal prosecution.

"This is very much an example of perfect being the enemy of good," Dr Caldicott said.

"They're trying to compare lab analysis to festival analysis. It's kind of like having the best mechanics in the world insisting on telling a Formula One driver how to drive their car.

"We're doing something completely different with the equipment they're used to."

A spokesman for ACT Health said the government had made it clear using drugs was neither safe nor legal.

He said while there was not a single solution to stopping young people taking drugs, data from a New Zealand festival showed 60 per cent of those who had their drugs tested decided not to take them.

"It is important to note that the main priorities of this trial are to improve safety and to reduce harm. We realise that even with police presence, people will still take drugs," he said.

"Pill testing is a proven way of helping people make a smart choice for their own wellbeing.

"Pill testing staff are armed with a range of helpful relevant information to provide young people while they take their drugs – an opportunity which would otherwise not have been made available."