For the young Vietnamese dope smokers rolling up outside a smart Hanoi cafe, local cannabis is just not good enough. As with their Adidas caps, iPhones and Sanskrit tattoos, so with their choice of bud: only foreign will do.

Potent marijuana grown indoors in Canada and the United States is easy to buy in Hanoi and Ho Chi Minh City, say regular smokers, and sells for up to 10 times the price of locally grown weed. That’s perhaps surprising given that marijuana is easy to cultivate regionally, and bringing drugs across continents is expensive and risky.

Some experts say the trade can be explained by the dominant role Vietnamese diaspora gangs play in cultivating the drug in western countries, making sourcing the product and smuggling it to Vietnam an easier proposition than it might be otherwise.

The characteristics of cannabis use in the country also drive the trade. The drug is used mostly by foreigners and well-heeled Vietnamese, who are prepared to pay for quality. Vietnamese have long shown preferences for imported goods of all kinds — and it appears cannabis is no exception.

Regardless of the reasons, its availability in Vietnam is a sign of how hydroponic growing techniques have shaken up the global marijuana business. In the 1960s and 70s, marijuana went from plantations in countries such as Thailand, India and Morocco to wealthy consumer markets in the West. Now, many western countries are self-sufficient in the weed because of indoor cultivation, and export is on the agenda.

Western-grown cannabis is also appearing in Japan and South Korea. Unlike Vietnam, both are wealthy, developed countries with climates ill-suited to cultivation. They too have seen a shift in supply from countries in the region such as India and Thailand to North America and Europe, law enforcement authorities there say.

The smokers sitting outside the Hanoi cafe, a short walk from the city’s famed French-era Opera House, seemed proud they were able to buy foreign, expensive buds, boasting their city was like a “mini Amsterdam.” But as the tightly rolled joints went round, they struggled to explain why western weed was available.

“Some people raise cows,” said one, a tattoo shop owner with a passion for big bikes and Facebook. “Other people prefer to buy steak at the market. ” Like other smokers interviewed for this story, he declined to give his name because cannabis is illegal in Vietnam.