BANGKOK: Australian Brodie Smith was convinced a radical treatment using an African shrub would cure his craving for illegal drugs and turn his life around, even though it is banned in some countries.

''Hey Mama Bear, I know it's been a while since I have actually seen or spoken to you . . . sorry, but I think it was mainly to do with me being ashamed, as once again I was on drugs and being around negative f***wits,'' he wrote to his mother on Facebook, only days before he stopped breathing, his eyes wide open while lying on a bed in a $19-a-night guesthouse on a remote Thai island.

Smith, 33, assured his mother that even though it sounded unbelievable because the plant called Ibogaine is hallucinogenic and is treated as a party drug, African tribes have been using it in its natural form for centuries in a rebirthing ceremony.

''It has a 92 percent chance of people not using [drugs again] within the first six months,'' he wrote.

The night before he died in front of his girlfriend, Kara Spark, on the island of Ko Phangan in the Gulf of Thailand, Smith had told her he wanted to marry her as he held her in his arms and the couple repeated their love for each other.

''It was the best feeling I ever felt,'' Spark says, adding that she and Smith made plans that night to have babies and get new tattoos to mark a ''new beginning'' for them both.

There are conflicting accounts about what happened in the following hours before Smith died in room four of the Utopia bungalows on the first morning of what was supposed to be a $5300 four-day Ibogaine treatment program for the couple from Western Australia.

But Smith's death has prompted calls for an inquiry into the use of Ibogaine, which is illegal to import into Australia without a licence and has been illegal in the United States since the 1960s because of severe side effects such as hallucinations, seizures and fatal heart arrhythmia and brain damage in patients with prior health problems.

Spark, 25, says she and Smith arrived on Ko Phangan on October 20 and the treatment began the following morning.

She says they first drank a lot of water and then were given an initial anti-nausea dose of Ibogaine in capsule form at 8.30pm, and more at 9am.

''I wanted to lie on the same bed as Brodie but they said I could not do so as it could be dangerous if he flailed around,'' she says.

Spark says about 11.40am Smith was given two blue hexagonal pills which he was told were valium that would put him in a ''sleep-like state''.

Some users say the plant creates dreams that give them insights into their addictions and visions that help them overcome negative emotions and fears.

But Spark says that 20 minutes later she saw that Smith was having trouble breathing.

''His breathing was heavy. He was short of breath. Then he stopped breathing. He was staring at me with his eyes wide open,'' she says.

Spark says she applied cardiopulmonary resuscitation until she could not physically do it any more.

But American Mike Picone, director of Ibogaine Thailand, which runs a treatment centre on Ko Phangan, denies that Smith ingested Ibogaine.

''Brodie was coming to fight a methamphetamine addiction and was required to be off all drugs for at least five days prior to doing Ibogaine,'' Picone says.

''Brodie Smith actually died in his hotel room. He overdosed from injecting illegal narcotics that he smuggled into Thailand from Australia before his scheduled Ibogaine session could take place,'' he says.

''After he died his girlfriend, Kara, produced a freshly used syringe and gave it to the police as she was reporting to them that he had shot up in the shower and overdosed.''

Spark denies this.

Police on Ko Phangan are known to play down tragedies involving foreigners on the island which is famous for its out-of-control full moon parties.

A police report into Smith's death cites an ''initial investigation reveals that prior to the deceased having a seizure he went to the bathroom and was using a needle to inject something into his body, causing him to have the seizure and pass away''.

A death certificate states that Smith died of a heart attack after taking narcotics.

But hospitals on Ko Phangan are little more than clinics and Smith's family has not been able to obtain the results of any forensic tests.

Picone, whose company is registered to sell pharmaceutical and medical goods, says that although Smith's death was not Ibogaine-related ''we have increased our screening process and repeatedly ask [clients] if they followed the pre-treatment instructions exactly, to the point of being incessant.

''We have also increased our warnings about the negative outcomes that can happen if our pre-treatment instructions are not followed,'' he says.

The use of Ibogaine is unregulated in Thailand.

In Australia, Smith's mother, Dianne Tucker, is calling for Australian authorities to investigate the death of her son and the use of Ibogaine.

Global Ibogaine Therapist Alliance, which advocates the use of Ibogaine to cure drug addiction, has begun its own inquiry.

''I don't want this to happen to anyone else's child,'' says Tucker, who works as a coordinator for the Ngaringga Ngurra Aboriginal Corporation in Halls Creek, Western Australia.

''The parents of anyone with an addiction problem have usually been to hell and back, dealing with all the traumas that come with drug use,'' she says.

''This Ibogaine was offered as a cure, and I was so excited, until I looked it up.''

Tucker says she found out that Smith and Spark were going to Thailand only the day before they flew out.

''I was excited for Brodie, that life was going to change . . . he was in love and wanted to have a family,'' she says.

''He knew that could never happen while he was using drugs.''

- with Andrew Drummond