VANCOUVER - New figures released by British Columbia's coroners service suggest fewer people are dying from overdoses overall but an extremely powerful opioid is increasingly present in those who die.

The BC Coroners Service says the monthly average for suspected illicit drug deaths between January and the end of March this year was 89, down almost one-third from the same period last year when the average was 132 people a month.

"Really since last November we've seen year over year decreases in the total number of illicit drug deaths in B.C., so that's a sign for continued cautious optimism," spokesman Andy Watson said.

But a synthetic opioid known as carfentanil, believed to be 100 times more toxic than fentanyl, was detected in nearly double the number of deaths in the first quarter of this year compared with the full year in 2018.

Carfentanil was found in 64 deaths by the end of March this year, compared with 35 for all of 2018, the coroners service said.

Fentanyl and its analogues, including carfentanil, were detected in almost 85 per cent of suspected illicit drug deaths in the first quarter of 2019, which is a rate slightly lower than last year.

"When you're looking at that level of toxicity and then you look at carfentanil being detected in over one quarter of the deaths for 2019, that's a fairly significant rise," Watson said.

There were no deaths at supervised consumption sites or drug overdose prevention sites, the data shows.

Watson said the overall decline in overdose deaths suggests that some of the interventions - including the prevention sites, education and opportunities for drug users to test their supply - are working.

"It's a positive sign, I think it speaks positively to the inventions that have been put in place," he said.