The Islamist group which controls much of southern Somalia has banned the popular stimulant khat, a day after protests in which one person died.
Islamist leader Sheikh Sharif Sheikh Ahmed said khat was a bad influence. Many Somali men, especially gunmen, spend hours chewing it each day.
He also warned squatters to vacate public buildings they have occupied.
After 15 years of conflict, many ministries are full of people who have fled fighting in their home regions.
Eyewitnesses say one person was shot dead by Islamist fighters on Thursday following protests over khat shortages.
About 60 khat vendors burnt tyres and threw stones in protest at shortages of the drug since a ban on flights to Somalia from Kenya, where most khat is grown.
"From today onwards we have banned khat in the areas we control," Mr Ahmed said.
Stimulant, making the user more alert and talkative
After a few hours, it produces a state of calm
A chemical found in khat could boost the power of men's sperm
Long-term use can bring on insomnia, heart problems and sexual problems
Can bring on anxiety and aggression
"Dealers found in possession of khat will pay 7 million Somali shillings ($5,000) and the khat will be burned. This substance is badly influencing our people."
The Islamists have burned two big khat consignments flown in this week to make up for the lack of Kenyan khat.
Kenya imposed the flight ban because of security fears.
There were six flights a week from Nairobi to Mogadishu and services to three other towns and many more khat flights each day.
The BBC's Hassan Barise in Mogadishu says a dusk-to-dawn curfew has been imposed on the city following Thursday's protests.
Mr Ahmed's call for squatters to vacate government buildings is seen as an attempt to restore normality to the shattered nation.
"Such buildings would be part of Mogadishu's reconstruction and we call for people to vacate the premises for common interest rather than considering their personal advantages," he said.
Some 800 families live in the old headquarters of the national airlines
But some question where people could go to.
Shelters made from plastic sheets and pieces of cardboard have been erected in the grounds of many public buildings.
Offices, too, have been taken over, with several families sharing a single room, in which the windows and fittings have long since been broken or stolen.
The Islamists have taken control of most of southern Somalia since seizing the capital.
Many Mogadishu residents have welcomed their rule as they have brought law and order to the city after years of anarchy.
In some parts of the country, Islamists have been closing public cinemas and, according to some residents, enforcing strict dress codes.
There are fears of a regional conflict starting in Somalia, as Ethiopia backs the weak interim government based in the city of Baidoa and its rival Eritrea is accused of arming the Islamists.