Swiss health authorities on Tuesday approved the launch of a pilot project for the recreational consumption of cannabis in Basel this summer.

About 400 people in the city will be allowed to buy cannabis from select pharmacies in Basel in late summer, the city's government said.

They will be questioned regularly about their usage pattern and physical and mental health.

The Swiss Federal Office of Public Health said the idea was to increase understanding of "alternative regulatory forms" or regulate the sale of cannabis at pharmacies because so many people consumed the drug.

The aim is to test whether consumption of the drug changes when it can be bought legally.