However, one of the study's authors said efforts by law enforcement to disrupt the illegal drug trade on the dark web was in some instances still "like a game of whack-a-mole".
The joint report from the Australian National University and the Australian Institute of Criminology found the shutdown of marketplaces from international law enforcement agencies affected the supply of opioids in other dark web markets.
The study examined eight such marketplaces on the dark web for almost a year during 2019, with researchers tracking the number of individual sellers, along with price and availability. Report author emeritus professor Roderic Broadhurst from the university's cybercrime observatory said the impact of police seizures and shutdowns were complex and subtle.
"We found evidence that shutdowns resulting from transnational police operations dispersed and displaced markets, vendors and buyers and it also reduced the availability of these drugs and their prices rose on the markets," Emeritus Professor Broadhurst said.
"The markets' response to law enforcement can be seen to be like the game whack-a-mole, with markets popping up somewhere else if one is closed down. And when they pop up again, they are reshaped." Throughout the course of the year, more than 4100 different opioid vendors were identified as operating on the dark web, where 74 per cent of them only operated in one market. About 19 per cent of those also sold fentanyl, a synthetic opioid that can be up to 80 times more powerful than morphine.
Of those that sold fentanyl, one-quarter of those also advertised carfentanil, a powerful opioid that was originally designed to sedate elephants. During the survey period, the median price for opioids sold on the dark web peaked at as much as $429 per gram.
According to the report, some dark web marketplaces, such as one based in Italy called Berlusconi, saw significant growth after other markets closed down. However, once it had been taken down by police, there was a significant decrease in overall listings on that market.
Berlusconi had the highest number of opioid listings on the dark web of the marketplaces surveyed, making up more than one-third. Emeritus professor Broadhurst said dark web markets had continued to evolve and presented unique problems to authorities.
"When there is a crackdown, there is a knock-on effect. It is like a searchlight and markets become aware that they are going to get a bright light shined on them for that particular product, especially high-risk products such as fentanyl," he said.