For Imam Yahya, one of the last kings of Yemen, qat was a delight, something to be praised in his poems. For his adversary, the revolutionary Mohammed al-Zubayri, the plant was "the devil in the shape of a tree."

That hardy tree -- famed among farmers for its drought resistance and whose leaves, when chewed, act as a psychoactive stimulant -- is today an integral part of Yemeni life. On average, 72 percent of Yemeni men chew the bitter leaves of the qat plant. The qat sector provides employment for one in every seven working Yemenis. The income qat provides allows many to remain in their rural hometowns instead of drifting into the cities to seek work. In some highland districts, over 90 percent of farmers are involved in qat agriculture.

Social life in Yemen revolves around qat. It is an accepted habit across all strata of society. Even afternoon sessions in the ministries or the consultative assembly are accompanied by chewing. Qat relaxes the chewer and helps stimulate mutual understanding and companionship. But there are also heavy social pressures to chew: Yemenis who might wish to abstain, for financial, family, or health reasons, fear exclusion and loss of respect.

Over the years I have observed how the chewing habit has proliferated in southern Yemen, in areas like Hadramawt, al-Mahrah, the Socotra Archipelago, where it was banned prior to the country's 1990 unification. I saw how the habit took hold of the coastal population and then slowly crept up the wadis to the herders of the highlands, how it spread from soldiers to fishermen, from traders to farmers, from adults to adolescents, and from husbands to wives. I watched how qat ravaged these regions' unique culture and how it changed social customs and society, how traditional leisure pursuits disappeared and how values and ethics have become diluted.

I have known Yemen for 20 years, have taken part in innumerable qat chews, and have interviewed several thousand people on the qat issue. For me, the leaves of the qat tree are not a narcotic drug. I hold the firm belief, however, that they are much more than the "mild social stimulant" to which literature so often refers. In my book, Politics of Qat -- The Role of a Drug in Ruling Yemen, I argue that qat is a potent social drug, holding Yemen and Yemeni life firmly in its grip.

Peer Gatter/The Politics of Qat

In 1970, only an estimated 7,000 hectares of Yemeni land were devoted to qat farming. But with the introduction of new irrigation technologies to Yemen in the 1970s, qat production exploded. Official figures from 2009 estimated that qat farming took place on 153,000 hectares, or 12 percent of Yemen's agricultural land, but many researchers believe the actual figure may be around double that.

In most other Arab countries, as well as in much of the West, qat is considered a drug, but in Yemen there are effectively no qat-control laws. Since the 1970s, the tree's vague legal status has been part of the bargain struck between the ruling regime and the restive highland tribes that produce most of the country's qat, and they would fiercely resist any measures to cut back production. Today, the state still engages in the occasional anti-qat campaign, but mainly for show -- a demonstration for fellow Arab countries and the aid community that is seldom of any real consequence.

Above, qat trees cover the hillside in the village of al-Mudmar in the Haraz Mountains.

Peer Gatter/The Politics of Qat

For Yemenis, qat is one of the sole unifiers of a very divided country. The chewing habit is one of the few things that Zaidi tribesmen, a Shiite sect of the northern highlands, have in common with Sunni merchants of the southern port city of Aden, who adhere to the Shafii doctrine. Many Yemenis think qat -- with its ability to form and cement strong bonds -- has helped facilitate mediation of many of the country's tribal conflicts.

Above are two men who have formed a qat friendship in Yemen's mountains.

Peer Gatter/The Politics of Qat

Leisure time without qat is unthinkable for most Yemenis today: a lonely, miserable, boring experience, something to be dreaded. Here, residents of the fishing town of al-Luhayya on the Tihama coastal plain pass a communal afternoon chewing.

Peer Gatter/The Politics of Qat

Chewing qat is often thought of as an idle pastime -- a habit that leads to lethargy and complacency. But it is also a stimulant, and many workers and craftsmen, such as these blacksmiths in the old city of Sanaa, use qat to help boost their stamina during their working hours.

Peer Gatter/The Politics of Qat

Above, a qat merchant in the highland village of al-Jabin shows off his merchandise. For qat connoisseurs, the choice of the right leaves is an art comparable to the selection of a good wine. Each strain of qat has its own characteristics. There is Sawti qat, to chase away fatigue. Pricey Hamdani qat is gentle and won't produce a headache the next morning. "Wedding night" qat can help one perform one's marital duties, while a potent strain from the Dhamar area dubbed "qat Saddam Hussein" is said to produce strength. The qat merchant above is holding Raymi qat grown in Raymah governorate.

Peer Gatter/The Politics of Qat

Above, qat sellers man their booths in the Suq Farwa market in the Shu'ub quarter of Sanaa. The Farwa market -- Sanaa's first modern qat market -- was build outside the old city walls in 1973.

Peer Gatter/The Politics of Qat

In Yemen, qat is a strategic commodity, used to buy allegiances and quiet a potentially restless populace. Qat was freely distributed by President Ali Abdullah Saleh's regime in return for votes at election time, and during the 2011 Arab Spring, the so-called "qat weapon" was deployed one last time, with millions of dollars of qat distributed to tribesman and others on the margins of Yemeni society to encourage them to come out to demonstrate in favor of Saleh. Here, in Sanaa's Tahrir Square, partisans chew late into the night in a pro-Saleh "tent city."

Peer Gatter/The Politics of Qat

Above is a shop in the weapons markets of Jihana in southeastern Sanaa governorate in the Kawlan tribal area. The store sells guns, grenades, rocket launchers, and land mines.

Under Saleh, the tribal areas were given special qat-related privileges as part of their compact with the government. Qat taxes were lowered in some areas, while territories of certain allied tribes -- the Sanhan, Hamdan, and Bilad Ar-Rus areas, for example -- were freed from qat taxes altogether. Import restrictions were placed on Ethiopian qat, while subsidies were provided for the irrigation equipment and diesel that farmers need for qat production.

But the incomes from the now-subsidized qat industry have helped undermine central government authority in these tribal areas. Qat money has helped these regions build up true tribal armies, equipped with heavy weaponry. The money also frees tribal areas from dependence on the patronage system that the regime relies on so heavily for governing leverage in other parts of the country.

Peer Gatter/The Politics of Qat

Even Yemen's elite special guards, seen here on patrol in the Marib governorate, are hooked on qat, claiming that its stimulating effects help them stay alert.

Money from qat sales is helping to finance the Houthi rebellion in northwestern Yemen, which many of these special guards spend their time working to contain. The Houthis make most of their money from qat smuggled into Saudi Arabia; the value of the illicit qat trade between Saudi Arabia and Yemen is estimated at around $1 billion a year.

Peer Gatter/The Politics of Qat

Qat is believed to have been introduced to Yemen from Ethiopia in the 13th or 14th century. The three qat trees pictured above, located in Wadi Zahr, near Sanaa, are a rare sight: Some 80 feet tall, they may be close to 200 years old.

Peer Gatter/The Politics of Qat

Yemeni-Jewish carpeter Yusuf Said grows qat and tomatoes in his small backyard in the town of Rayda in Amran governorate. Yemeni Jews brought their love of qat to Israel when some 49,000 Jews left the Arabian Peninsula in 1949 and 1950. Today, qat is grown on the plains southeast of Tel Aviv and is shipped daily to Israel from Ethiopia.

Peer Gatter/The Politics of Qat

Even Yemen's architecture has been shaped by the country's qat habit. The top room of most Yemeni houses is the mafraj, where in the afternoons, chewers gather to enjoy the view through tall glass windows. Here, a square mafraj has been added to the top of the fortifications on an ancient clay tower house in Wadi Zahar near Sanaa.

Peer Gatter/The Politics of Qat

According to Yemeni tradition, it was the Sufi mystics who first used qat to help enhance their spiritual experience. Chewing in the shade of a mango tree, qat helps this pious man in Wadi Zabid concentrate on his Quran reading.

Peer Gatter/The Politics of Qat

The barra is a traditional dance that precedes qat chewing at wedding ceremonies. During the barra, participants swing their curved daggers, called jambiya; here, the author (right) participates in a celebration at the mountain village of al-Zafin near Kuhlan.

Peer Gatter/The Politics of Qat

A qat truck arrives early in the morning in al-Mukalla in the coastal lowlands of southern Yemen. Qat is not grown in this hot, humid climate and must be brought here over a distance of 400 miles on rugged roads. The leaves are brought from the northern highlands in moist burlap sacks to keep them fresh.

Prior to Yemen's unification, qat use in southern Yemen was either entirely banned, in areas like Hadramawt or Socotra island, or restricted to weekends, in areas like Aden. The liberalization of qat use in southern Yemen since unification has not been beneficial for the region. Spending on qat has skyrocketed, while spending on essentials such as food, medicine, and clothing has fallen off. Yemen's 2005-2006 household budget survey revealed that Yemeni families on average spend 10 percent of their budget on qat, while in poor households the share is closer to 40 percent. The same survey also showed that in southern governorates like Aden or Lahij, families spent 11 times as much on qat as they spend on education and up to six times as much as they spend on health care.

The desperate economic situation in areas like Abyan, Lahij, or Aden has made them fertile recruiting grounds for al Qaeda, and the situation appears likely to deteriorate further as long as the qat issue remains taboo for the central government. It's important for governments and donors from both Western and other Arab countries to understand the role qat plays in both development and security issues in Yemen in order to develop effective policy. Efforts to reduce qat consumption might over time be more effective in securing Yemen against militant Islam than measures to boost the drone program in the country.

Peer Gatter/The Politics of Qat

Above are Bedouin qat merchants in Harib, in Marib governorate in central Yemen. Prior to the early 1980s, chewing qat was perceived as shameful by local Bedouins, and as al Qaeda becomes increasingly powerful in Yemen's desert areas, it is once again trying to impose a qat ban. These efforts have so far been unsuccessful -- the chewing habit is simply too popular. Interestingly, while qat-related poverty may aid in recruitment for groups like al Qaeda, the drug's nationwide popularity may also boost resistance to militant Islam in Yemen. The popularity of the militant group al-Shabab plunged sharply in Somalia when it banned qat sales and consumption in the areas under its control.

Peer Gatter/The Politics of Qat

Above is al-Mukha, a once world-famous port that shipped "Mocha" coffee -- the word is derived from the port name -- to Turkey, Egypt, and Europe. Today, al-Mukha is a lethargic provincial town where ruins of richly decorated ancient mosques and merchants houses serve as a reminder of former prosperity. Coffee farming across Yemen has been displaced by qat farming. Qat trees are more drought resistant and can go for months without irrigation -- an advantage in a country increasingly exposed to the effects of climate change. In addition, qat farmers face no competition, as imported qat is banned in Yemen, while coffee farmers must sell their products on the volatile world market.

Peer Gatter/The Politics of Qat

It's not very clear what price Yemenis pay in their health for their national habit. Yemen has a high incidence of cancer -- often linked to pesticides ingested through qat chewing or water that has been contaminated by pesticides or chemical fertilizers. Awareness of the potential health impacts of qat is very low among farmers and consumers. According to the country's 2002 agricultural census, 72 percent of Yemen's qat farmers use pesticides, including highly poisonous ones that have been smuggled into the country and contain DDT and other toxic agents.

Peer Gatter/The Politics of Qat

For all their much-touted drought resistance, qat farming remains water intensive and often comes into competition with household water use. In many villages, including this highland village of Thula, qat farmers use fresh groundwater for irrigation, while the village population has no access to safe drinking water and must use surface water from cisterns.

Peer Gatter/The Politics of Qat

Villagers uproot qat trees in the village of al-Amal in the Haraz Mountains. Following a fatwa by the leader of the Buhra sect, Syedna Mohammed Burhanuddin, some 400,000 qat trees in the Buhra stronghold of the eastern Haraz Mountains have been uprooted since 1999 and replaced with coffee. The Buhra sect believes qat is a social evil and that its cultivation and consumption should be outlawed on religious grounds.

Fighting against qat in Yemen is difficult. Being anti-qat is often perceived as being anti-social and non-Yemeni. Qat critics in southern Yemen have been told by security forces that to question qat is to question national unity. But the anti-qat movement has gained momentum since the 2011 revolution via Facebook and Twitter campaigns. For some, the fight against qat was seen as part of the fight against Saleh's corrupt regime.

The future of qat in Yemen is still unclear. The government remains afraid of both the highland tribes and general public unrest; moreover, many members of Yemen's political and military elite have investments in qat, which can produce staggering returns. Yemen still suffers from a lack of alternative pastimes, an absence of other viable and profitable economic activities, and a shortage of markets for alternative high-value crops. As the country heads toward a post-oil era -- Yemen's oil reserves are expected dry up as early as 2017 -- the qat sector will likely take on an even more outsized role in Yemen's economy, and the balance of power in Yemen will shift even further toward the highland tribes. Will the government be able to control the industry -- to get a grip on qat markets and produce real revenues from qat taxation? Or will Yemen follow in the footsteps of Somalia and become a country ruled by a drug?

Peer Gatter/The Politics of Qat