Australians are being warned they face jail sentences if caught importing party pills from New Zealand.
The benzylpiperazine-based pills are widely available in New Zealand, both in shops and online, but are banned in some Australian states including New South Wales.
Sydney drug squad commander, Detective Superintendent David Laidlaw, said New South Wales residents found in possession of the synthetically produced drugs faced two years in jail.
"We have identified a number of New Zealand-based companies advertising on the internet, which are supplying residents across Australia with these products," he told the Sydney Morning Herald.
Not all websites selling the pills advise overseas purchasers to check whether or not they are banned in their countries.
Some of the pills were being marketed as being particularly strong, including one called "Bolts", which was described as being "like a lightning bolt of pure energy straight to your brain".
One website said: "Bolts are guaranteed to make your jaws clench, your hair stand on end and your feet want to hit the dance floor. Bolts are the strongest energy pills legally available in the world today."
Australian police said benzylpiperazine was a synthetic drug developed as a potential antiparasitic agent and could produce an increased heart rate, nausea, headaches, fatigue, insomnia, seizures, confusion and mild memory loss.