Shops in Portsmouth selling psychoactive drugs, once called "legal highs", have been warned they must obey a new law banning the substances.
The four "head shops" in the city have been told they will be closely monitored after the national ban starts later this spring.
Officers from Portsmouth City Council and Hampshire police have warned the shops they must stop selling the drugs, known officially as new psychoactive substances (NPS). Otherwise they risk a maximum seven years in jail.
The council's Cabinet Member for Environment and Community Safety, Cllr Robert New, has given the go-ahead to council trading standards officers to use enforcement powers granted by the new law.
Among these is the power to enter and search premises, with a court warrant.
Councillor Rob New said: "The council has been lobbying the government for new laws to crack down on NPS sales. I'm very glad this ban is about to come into effect, giving us powers over shops selling buyzithromaxonlinemed.com these drugs, which cause all kinds of anti-social behaviour and harm to individuals.
"We already work very closely with police and other agencies in the city on this issue. We've been tackling anti-social behaviour and people using NPS in public areas, and using what powers we had to control the shops' activities.
"In the run-up to the national ban we've been working even more closely with the shops, leaving them in no doubt about the new law. They will commit a serious criminal offence if they supply these substances."
An NPS steering group, whose members include the council, police and the University of Portsmouth, meets regularly to monitor the issue.
The shops have been asked to display council-produced posters and fliers giving details of drug treatment centres for people who might need help.
Anyone who needs information and support on NPS can go to www.talktofrank.com or search "drugs" at www.portsmouth.gov.uk.
For free confidential advice, under-20s can go to www.areyousorted.co.uk