"This is one of (the) largest humanitarian challenges in scale and in scope that we face in the world," John Ging, operations director for the UN Office for the Coordination of Humanitarian Affairs (OCHA), told reporters here at a briefing, Xinhua reported.
"It is extremely fragile there at the moment," Ging said.
"Khat really is an issue that is undermining the development of this country in a fundamental way," Ging said. "It affects the health; it affects the economy; it affects so many aspects of the functioning of society."
Khat, a shrub whose young leaves contain a compound with effects similar to those of amphetamines, is popular in many countries of the Arabian peninsula.
According to media reports, about 90 percent of men and one in four women in Yemen are estimated to chew khat.
Khat chewers experience euphoria followed by depression. Khat can also affect sleep, leading to rebound effects such as late awakening, decreased productivity and day-time sleepiness.
The effect of khat on the cardiovascular system is rather less dramatic, but increased heart rate and blood pressure are common side-effects, making khat very harmful for hypertensive patients.
Khat an issue that is undermining the development of this country
On the drug's debilitating effect, Ging said the leadership in Yemen raised concern over khat because of its effect "as a particular problem that requires a completely new approach" because it was "fundamentally undermining the functioning of society in every dimension, socially and economically and it also links in to security as well".
"Seventy percent of the water resources are estimated to be used for the growing of this drug, highlighted to us by so many people," he said. "There needs to be a plan to address this scourge."
"What was quite impressive for us was that in our engagement with the political leadership, with civil society leadership, with people themselves, they were all pointing to this problem and they were also asking us to engage more effectively in support of the country's leadership to have a strategy with this growing problem, " said the OCHA operations director, who visited Yemen June 22-26.
"It's already a mega-problem and it is even getting worse," Ging said. "People were appealing to us to help them with that."