Australians have access to mass amounts of potent drugs online, equivalent to "billions of doses" every day, according to a new study from The Australian National University (ANU).
The report found "alarming" amounts of synthetic opioids such as fentanyl and carfentanil available on the dark web.
Carfentanil is not for human use and was originally designed to sedate elephants.
The researchers say the report lifts the lid on a significant new synthetic opioid market on the dark web.
"We are on the brink of a new opioid epidemic driven by synthetics like fentanyl and carfentanil that are driving a greater risk of overdose deaths," said lead author Professor Roderic Broadhurst, from the ANU Cybercrime Observatory.
"Fentanyl is a designer synthetic opioid about 100 times more powerful than morphine," said Professor Broadhurst.
"The average dose of fentanyl is 200 micrograms. We found millions of doses of fentanyl available to buy every day.
"Carfentanil is 10,000 times more powerful than morphine and there are alarming amounts of it available online."
"We were shocked by the amount of Carfentanil we found. Billions of doses are available online on any day."
Professor Broadhurst says fentanyl is being used by criminal networks to lace heroin and create synthetic heroin that is changing the landscape of narcotic sales.