The habit of chewing qat leaves (Catha edulis) is widespread in certain areas of East Africa and the Arabian Peninsula mainly Yemen. It has pleasurable central stimulant properties, which are commonly believed to improve work capacity and counteract fatigue.

The consumption of qat causes acute effects on the central nervous system leading to exacerbation of symptoms in psychiatric patients, on the cardiovascular system leading to hypertension and increased risk of cardiovascular events particularly in hypertensive patients and on the male urinary bladder neck leading to weak stream of micturition.

The effects on other parts of the body such as the mouth, oesophagus and gastrointestinal tract as well as foetal development seem to be related to chronic intake. There is concern about hazards related to the pesticides used in qat cultivation.

Several studies conducted over the past few years on qat consumption effects revealed that consumers suffer cancer in different parts of the body because of the pesticides and fertilizers used for qat cultivation.

Officials in the Yemeni Ministry of Public Health and Population recently explained that illegal pesticides used in the cultivation of fruit, vegetables and qat cause thousands of cancer cases annually.

Several pesticides were toxic and prolonged use could cause serious diseases among qat consumers, including cancer, said Nadim Mohamed Sa'eed, Director of the Sana'a-based National Cancer Center 

According to Sa'eed, the U.N. Integrated Regional Information Networks reported that about 30 percent of Yemeni cancer patients have mouth and gum disease.

"This is really a frightening figure and represents one of the world's highest rates for mouth and gum cancers," the health official continued.

Ahmed Al Haddad of Assistant Professor of Sana'a University Medical College said 70 percent of pesticides used on qat cultivation are smuggled into the country illegally.

"The chewing of qat is one of the main causes of cancer of the digestive system and kidney failure and that it is partly due to the pesticides sprayed on qat plants for the purpose of fast growth of the qat leaves," Al-Haddad added.

Qat and Cancer

Since qat use is widespread and often persists throughout adult life, a number of studies have been made on the toxicological aspect of habitual qat use.

Owing to its mode of consumption, qat frequently affects the oral cavity and digestive tract. Tumours of the oral cavity (lower maxilla, buccal mucosa and lateral surface of the tongue) were reported in 13% of patients seeking treatment over a two year period in a clinic in the Yemen's western city of Hodeidah. Most of them had been habitual qat chewers for more than 20 years, and some of them also take shamma (ground tobacco).

A similar review of mouth cancers presenting over a two-year period in the Asir region of Saudi Arabia showed strong circumstantial evidence linking the long term use of qat with an increased rate of oral malignancies.

Tannins in qat can thicken the mucosa of the oropharynx and oesophagus, and may be carcinogenic. A recent study in Yemen has shown that oesophageal and accounted for as much as 6% of all patients who had an upper gastrointestinal endoscopy (183 out of 3064 patients) over a period of one year.

A preponderance of women with carcinoma of the mid-oesophagus was noted, previously only recorded in areas of high prevalence of oesophageal carcinoma. A high frequency of qat-chewing and water-pipe smoking was found for both men and women to be linked with a group of tumours of the gastro-oesophageal junction or cardia. This apparent association with carcinoma of the lower oesophagus might be related to the qat-induced delay of gastric emptying with a subsequent increased risk of gastro-oesophageal reflux and Barrett’s oesophagus.

The effect of chewing qat on the mucosal histology of the upper gastrointestinal tract was explored in Yemeni patients complaining of dyspepsia. Regular daily qat chewing was not associated with any major effect on the oesophagus or stomach but duodenal ulcers were commoner in chewers. This may have been associated with the high prevalence of smoking in this group.

Gastric type mucosa at the lower end of the oesophagus is thought to increase the risk of developing adenocarcinoma by 30–125 fold. Although its presence was not related to the intake of qat, its overall prevalence in Yemeni patients was comparatively high (18%). 

Qat provides farmers with income, so they use pesticides and fertilizers to make the plant grow faster. Farm workers are most at risk, as are chemical sprayers, people who live near farms where methyl parathion, which can affect the central nervous system, is used and those who enter fields too soon after spraying.