Police say there's no telling what mix of potentially lethal chemicals went into any given batch of ecstasy, which is why one ex-drug dealer says he used to test his wares on vulnerable Downtown Eastside residents.

Jason, a former dealer who asked CTV News not to use his last name, says he's seen amateur criminals try to cook up their own ecstasy, and "that's when you know you have to find testers."

Those "testers" were drug addicts, whom Jason and his associates used as guinea pigs to determine the toxicity of their pills.

"They try the drug and come back and tell us how it is," Jason said. "If we don't hear back from them and they're gone, hey, probably not good stuff."

He also found testers on Kingsway and through dial-a-dope lines.

There were 16 ecstasy-related deaths in 2011, according to B.C.'s chief coroner, and another three have died after taking the drug so far this month. Five of those have been linked to a toxic chemical called paramethoxymethamphetamine, or PMMA.

PMMA is a hallucinogen considerably more hazardous than methylenedioxymethamphetamine, or MDMA, the active ingredient in ecstasy. It can cause seizures and elevate body temperatures to dangerous levels.

Jason says a crackdown on the sale of the chemicals used to make ecstasy has led to the changes in the drug's composition.

And Mounties confirm there's now another drug in the mix. Benzylpiperazine, or BZP, is a recreational drug that has similar effects to MDMA, but has yet to make Canada's list of controlled substances – making it technically legal.

"The federal government [and] Health Canada are moving right now to control, to schedule BZP to make it illegal," said Burnaby RCMP Sgt. Scott Rintoul.

In the meantime, Rintoul warns the drug may be as dangerous as its illegal counterparts when mixed with other chemicals.

"I've heard anecdotally there have been deaths associated to BZP in combination with other drugs," he said.

Another possible ecstasy-related fatality is under investigation in B.C., as is one in Alberta, where five recent deaths have been linked to ecstasy and PMMA. But Jason says the tragedies don't affect dealers' bottom line, or the steady demand for the party drug.

"If one person dies, there's another person," he said. "Nowadays it doesn't matter. There will always be kids, people wanting drugs."

With a report from CTV British Columbia's Michele Brunoro