A complete ban on the drug naphyrone is being introduced in Guernsey from Tuesday.
It is already illegal to import or export the powder but from 17 August anyone supplying or possessing it faces a prison sentence of up to 21 years.
Naphyrone is sold under the names NRG1 and NRG2 and is advertised as a plant food or pond cleaner.
A report by the UK's Advisory Council for the Misuse of Drugs showed naphyrone was more potent than cocaine.
It said the drug had considerable abuse potential and using it carried a high risk of overdosing.
The Misuse of Drugs Law will be updated to include it on the banned list of Emerging Drugs of Concern.