Read the main article on Kenyan Christians defending khat.

Khat use has rarely been studied clinically and “has largely escaped medical attention,” according to Farrah J. Mateen and Gregory D. Cascino, two doctors who wrote a 2010 study in Mayo Clinic Proceedings, the journal of the Mayo Foundation for Medical Education and Research.

“Chewing the leaves of the plant Catha edulis,” Mateen and Cascino wrote, “likely dates to times of antiquity and may predate the use of coffee.” They compare the active ingredient in fresh khat leaves, cathinone, to amphetamine, identifying it as having “euphoric and mood-altering effects among other health consequences.” (The cathinone in the plant deteriorates as the leaves dry.)

Mateen and Cascino’s study of nearly 1,000 khat chewers among more than 8,000 patients in Yemen suggests that khat may be a risk factor for death after heart attacks and similar coronary syndromes. The fact that most people who chew khat also smoke tobacco, they wrote, makes it difficult “in nearly every study on khat chewers” to know whether cathinone is the culprit in the health problems.

When Britain was considering a ban on khat, its Advisory Council on the Misuse of Drugs reviewed the available information and released a report in January 2013 saying that khat “is chewed to obtain a mild stimulant effect and is a less potent stimulant than other commonly used drugs, such as amphetamine or cocaine.”

Looking at the issue of medical harm, the council also noted the lack of clinical data. The evidence “is generally not strong and conclusive, and it is difficult to differentiate potential adverse medical consequences of khat use from other factors such as poor general health, concurrent smoking of tobacco, low health literacy in some user populations, and lack of access to health services.” The evidence “shows that khat has no direct causal link to adverse medical effects, other than a small number of reports of an association between khat use and significant liver toxicity.” On the basis of that evidence, the council advised against classifying khat as a controlled substance.

Nevertheless, in July 2013 the United Kingdom joined most of Europe, the United States, and Canada in banning khat, which has been used there mostly by immigrants from Somalia, Ethiopia, and Yemen, according to the BBC.