Health officials in Ottawa warn rave drugs are a "very big" public health concern after one woman died and another was in a coma due to pills taken last weekend.

On Friday, Ottawa police said the women had taken rave drugs at two separate events between June 29 and July 1.

Police spokesman Const. Chuck Benoit said the drugs were believed to be ecstasy but autopsy results on the 19-year-old victim would provide more information. There were also tests being done on the 20-year-old woman in a coma.

Ecstasy pills, which contain MDMA as their main chemical, are pictured in this undated handout photo courtesy of the United States Drug Enforcement Administration (DEA). (Reuters) Benoit said it's rare for police to see ecstasy overdoses lead to death, but it's a concern with so many large gatherings happening around the city.

Police and health officials are telling young concert-goers to be careful as festivals such as Bluesfest take over the capital.

Rosamund Lewis, the associate medical officer of health at Ottawa Public Health, said about 40 people die from overdoses each year. The overdoses are usually unintentional, she added, but the risk increases when people mix pills with alcohol and other drugs.

1 in 25 high school students uses ecstasy

Lewis said one in 25 high school students uses ecstasy. That adds up to about four per cent of students in the capital.

"That may not sound very high but … for every 25 high school students in this city, one of them is already using ecstasy. So in terms of a public health concern, it's a very big public health concern," Lewis said.

Benoit said the incidents happened at different locations — one in the east end and the second in the downtown area.

Now they're looking for witnesses to come forward to help learn more about what the women took and where they purchased the drugs.

Anyone with information about these incidents is asked to contact Ottawa police at 613-236-1222, ext. 5166.