Possessing khat, a plant used as a stimulant by Somali communities, has been made illegal in the UK.
The ban comes after members of Cardiff's Somali community previously called for khat to be outlawed while others say it does not have a negative effect.
But opponents to the ban say alcohol has a wider effect on people.
The move will stop the UK from becoming a hub for trafficking khat to countries where it is banned, says a minister.
Khat, which users say makes them feel more alert, happy and talkative when chewed, is now banned as a class C drug despite advice from the UK government's official advisers that it should not be classified.
However, Nasir Adam, a community regeneration officer in Cardiff, said he expected the majority of the city's Somali community would welcome the ban, saying excessive use has an effect on people's mental health and has caused the break-up of families.
He explained it was traditionally chewed by older men before its frequency of use increased and widened to younger members of the community.
And although he said the "community has been fighting for this" ban, he questioned whether police, health and council officials have done enough to prepare people for the change in law.