The findings of the study by Professor Keith Hawton of the Department of Psychiatry at the University of Oxford and colleagues is published in the journal PLoS Medicine.
The withdrawal of co-proxamol has not seen an increase in deaths involving other pain killers.
Co-proxamol, a prescription pain killer containing paracetamol and the opioid dextropropoxyphene, was implicated in a fifth of drug-poisoning suicides in England and Wales between 1997 and 1999.
It was withdrawn completely from use in the UK during the period 2005 to 2007, mainly in response to concerns over the drug’s widespread use for suicidal poisoning.
A previous study by the same research group showed a reduction in the number of co-proxamol-related suicides during this three-year withdrawal phase and no evidence of an increase in deaths from other prescription pain killers. The team have now looked at the longer-term effects of co-proxamol withdrawal.
Professor Hawton and colleagues assessed the impact of co-proxamol withdrawal in England and Wales by comparing data on pain relief prescribing and suicide rates collected between 1998 and 2004 with data collected between 2005 and 2010.
They found that on average, from 2008 to 2010, there were 20 deaths related to co-proxamol per year, including suicides and accidental poisonings. It was more than 250 per year during the 1990s.
The researchers found little evidence of a change in the number of deaths involving poisoning from other drugs after co-proxamol withdrawal, in spite of increased prescribing of these alternatives.
The findings suggest that the withdrawal of co-proxamol in the UK, and possibly elsewhere, should have major beneficial effects on suicide rates, though the authors note that they did not investigate suicides related to the use of multiple drugs or investigate whether suicides involving methods other than drug-related poisoning have increased since co-proxamol withdrawal.
‘Now that prescribing of the more toxic constituent of co-proxamol (dextropropoxyphene) has been withdrawn throughout Europe, and production has ceased in the US and Canada, the impact of this initiative should be evaluated on a larger scale,’ the researchers say.
The study was funded by the National Institute for Health Research with extra support from the Oxford Health NHS Foundation Trust and the Manchester Mental Health and Social Care Trust.