Leicester East MP Keith Vaz has urged the Government to abandon plans to make a herbal stimulant illegal.
Khat is popular among Leicester's Somali community and is currently legal.
However Home Secretary Theresa May has said the substance will become a Class C drug next year making it illegal to possess and supply.
Khat can create a high, increasing alertness, when it is chewed but there are suggestions taking it can exacerbate mental health problems, suppress appetite and increase blood pressure as well as cause insomnia.
Mr Vaz, who is chairman of the House of Commons Home Affairs Select Committee, said the decision to make Khat an illegal drug had not been made based on evidence or consultation.
He said the Advisory Council on the Misuse of Drugs concluded that no social or medical harm resulted from the use of khat.
He added: "Khat is a perfectly legal substance which is imported into this country and where there has been no example of the involvement of people who deal in khat in criminality, nor has there been the police saying it should be stopped."
