Patients receiving methadone treatment are most at risk of overdosing during the first four weeks of treatment, and in the month following the end of treatment, a new study has found.

Methadone treatment is used to treat dependence on opioids, such as heroin. People who are dependent on opioids are 10 times more likely to die prematurely compared to the general population.

It is widely acknowledged that the most effective treatment for this type of addiction is the prescription of legal, substitution drugs, most commonly methadone.

Researchers from the Royal College of Surgeons in Ireland (RCSI), analysed data from 2,899 people who had had been treated with methadone between January 2010 and December 2015.

During that time, 154 deaths occurred, 35% of which were drug-related poisonings.

The study found that the rate of drug-related poisoning deaths was over three times higher in the first four weeks of treatment. Furthermore, this death rate was more than four times higher immediately after the end of treatment.

"Identifying a higher risk at the beginning and immediately after the end of treatment highlights that retaining patients in treatment for longer periods will save lives.

"People often cycle in and out of treatment, thereby increasing their exposure to repeated periods of high risk," commented the study's lead author, Dr Gráinne Cousins, a senior lecturer at RCSI's School of Pharmacy and Biomolecular Sciences.

She said that closer monitoring of opioid tolerance before beginning treatment, as well as more effective methods of preventing relapse during the induction period, may lower this risk.

"Additionally, increasing patient awareness of the risk of overdose and increasing the availability of take-home naloxone may mitigate the risk of overdose during the high-risk periods, particularly following treatment cessation," Dr Cousins said.

Naloxone is an antidote used to reverse the effects of opioid drugs, such as heroin and methadone, if someone overdoses.

Details of these findings are published in the journal, Addiction.