Drug manufacturer Pfizer this month agreed to settle with 160 Australians who took its drug Cabaser to treat tremors associated with Parkinson's disease or restless legs syndrome between 1996 and 2010.

The agreement, ahead of a class action due to be heard in the Federal Court, follows a settlement last year for 32 people in a similar action against Aspen Pharmacare and Eli Lilly over their drug Permax.

Patients are expected to share in millions of dollars' compensation, with some losing hundreds of thousands of dollars on gambling binges after taking the drugs despite not having prior gambling problems.

Both Parkinson's disease and restless legs syndrome are neurological disorders caused by a lack of dopamine in the brain.

"Dopamine agonists" mimic the effects of dopamine, in some cases restoring a person's ability to control their movements.

But the chemical is also known to produce a "rush" which has been linked to risk-taking behaviours and addictions.

The class actions alleged that drug companies were negligent in selling the medicines in Australia without any or adequate warnings about side-effects.

Arnold Thomas & Becker partner Allanah Goodwin said this led people to go on "gambling and shopping binges and engage in bizarre hypersexual behaviour, without realising it was a side effect" of the medicines.

Clients who developed gambling addictions ranged from "a pensioner who might have lost a modest sum to professionals who had a lot more money to go through," she said.

Pat Galea, 65, lost about $700,000 on poker machines after taking both Permax and Cabaser for about a decade for restless legs syndrome, which creates an urge for sufferers to move their legs.

"I'd go any spare moment I was not working. If it was pay day I'd put most of it through and then realise I've got bills and rent and petrol to pay. As soon as I had any money it was gone," Mrs Galea said.

She separated from her husband and gambled away half the proceeds from the sale of their house, also selling her car to fund her addiction.

It took years for evidence to emerge about the drugs' side-effects and as soon as Mrs Galea stopped taking them, she lost the urge to gamble.

She has since reunited with her husband and enjoys time with her three adult children and four grandchildren. Asked whether the settlement came close to repaying what was lost, she laughed.

"It's a drop in the bucket. And that's just the money. What about years of life for my family? What about their suffering, let alone me?" she said.

Salvation Army financial counsellor Maria Turnbull was among the first to ask questions about a link between dopamine agonists and compulsive gambling after a bankrupt woman in her 60s came to her seeking food vouchers in 2006.

The woman told Mrs Turnbull that drugs she was taking for restless legs syndrome had led her to gamble, and she started looking into a possible link.

Mrs Turnbull has since met more than 100 people involved in the Australian class actions, including a man who developed compulsive sexual behaviour and is now on the sex offenders register. He needs permission to see his grandchildren.

"There are people I'm sure who have committed suicide over this. They haven't known it was the drug doing it. There are families that have been ripped apart," she said.

A spokeswoman for Pfizer Australia said that while the parties had agreed on a proposed settlement, this was subject to Federal Court approval, and the drug company was therefore unable to provide further comment.