A Queensland coroner has recommended that drug manufacturer Pfizer put a warning label on the quit-smoking drug Champix and that toxicology tests for the drug be conducted on all people who died by suicide, after a mother's four-year fight to prove that the drug contributed to her son's death.

Timothy John died in April 2013. He was just 22.

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His mother Phoebe Morwood-Oldham spoke to 7.30 in 2015 and gathered 49,000 signatures on an online petition before the Queensland coroner reopened an inquest into Timothy's death.

Timothy left a suicide tape for his mother on her kitchen bench and next to it he left a box of the drug Champix — he'd only been on it for eight days.

"Mum, I love you with all my heart. Peter, you're the best brother I could ask for," Timothy said on the tape.

"I know it doesn't make sense right now, but it's for the best, trust me.

"I'm losing my mind, I'm going crazy. I love you both."

Ms Morwood-Oldham said the strange behaviour started a few days into his treatment.

'I hope it has helped save other people'

The Queensland coroner today found that Ms Morwood-Oldham's suspicion that the drug had a role in Timothy's decision to end his life was right.

"I find that Champix contributed to Timothy's death," coroner John Hutton said.

He also found that Timothy's doctor, Oliver Yang, "did not provide adequate care" to Timothy when prescribing Champix.

The anti-smoking drug, Champix, was found to have played a role in Timothy John's death. ( Flickr: Adam Roe )

"If Timothy's family had been informed by Dr Yang (or by warnings within the Champix packaging) about the need for Timothy to stop taking Champix and to contact a doctor immediately if he exhibited neuropsychiatric symptoms, it is likely that his family would have taken appropriate earlier action, and it is possible that Timothy's death may have been avoided," Mr Hutton said.

Ms Morwood-Oldham told 7.30 she was shaking after the finding came down.

"I literally hugged everybody in the courtroom," she said.

She said it had been a difficult battle and the power imbalance between her and a multinational pharmaceutical company meant she expected the finding would not go her way.

"Pfizer is a multi-billion-dollar company and I'm just one person and they've got all the resources," she said.

"I felt like David against Goliath.

"It means that I've achieved everything I wanted to achieve.

"We're going to go down to the grave this afternoon and just say thank you to Timothy.

"It's sort of vindicated Timothy's death, but I hope it's also helped save other people."

'Certain aspects of the product labelling are inadequate'

In the US, from 2009 the drug carried a so-called black box warning about side effects, but that warning was removed by the US Food and Drug Administration in December 2016 after it was deemed no longer necessary.

Pfizer settled a class action launched over a range of side effects by thousands of Champix (known in America as "Chantix") users — the settlement was said to be about $US300 million.

But in Australia, doctors have until now been sceptical about the link between Champix and suicide.

The Therapeutic Goods Administration (TGA) had said that warnings about the drug were on Pfizer's website and available online.

"I find that certain aspects of the product labelling and instructions provided with Champix are inadequate and some improvements may be made," Mr Hutton said in his findings.

The coroner recommended that Pfizer, in consultation with the TGA, make improvements to the Champix labelling, consumer medicine information leaflet and product information document.

Mr Hutton also recommended all state and territory forensic pathology services follow Victoria's lead and conduct "routine toxicology screening for [Champix] in relation to suicides and suspected suicides".

However, the coroner said that he was unable to determine the level of contribution the drug had on Timothy's death due to his pre-existing mental health condition.