The pills come in a pretty rainbow of colours – purple, pink, orange and green – and boast flavours such as chocolate and strawberry to mask the bitter concoction of drugs inside.

But far from being the confectionery it is designed to resemble, yaba – which translates to "crazy medicine" – is a mix of methamphetamine, better known as crystal meth, and caffeine that can leave users awake for days.

Long the drug of choice for adults in Thailand, yaba producers are now trying to sell it to children through Facebook, Thai authorities say.

"Yaba [producers] are trying to change their product to meet the demands [of] targeted groups," Dr Viroj Verachai, of the Princess Mother National Institute on Drug Abuse Treatment, recently told the English-language daily The Nation. "These flavours help the users take the drug more easily, but it could severely affect their [central] nervous systems."

Yaba tablets are small enough to fit into a straw and are generally swallowed, or crushed into powder and snorted, smoked or injected.

As the drug has gained popularity over the years, so has its potency – increasing in its methamphetamine concentration from 20% to as much as 95% for yaba's more pure, crystalline form, "ice".

Verachai said that roughly 75% of those seeking treatment at drug rehabilitation centres in Thailand were yaba users, with the remainder seeking help for ice. Doctors warn that chronic use can lead to hallucinations, anxiety and psychosis.

As individual yaba tablets are sold for up to only 200 baht (£4) each, the drug is easily accessible and highly popular with various social classes in Thailand. It is said to help factory workers toil long hours and socialites party all night long.

In May, a 41-year-old monk told police he took the drug to help him lose weight, while in July one of the stars of the popular teen series Hormones caused a scandal when photographs of her using yaba went viral.

The drug is produced predominantly in the Golden Triangle, a remote, jungle-studded area where Thailand, Burma and Laos join and ethnic armed militias rule a trade estimated to be worth $8.5bn (£5.5bn).

Data from the UN's Office on Drugs and Crime estimates that about 1.4bn yaba tablets are produced there each year; a 2011 report stated yaba was the drug of choice in Thailand, Cambodia, Laos, Brunei, the Philippines, Japan and South Korea.

Yaba has made its way to North Korea, where it is reported to be mass-produced in government factories to be sold in China then traded back from there and consumed by up to 50% of adults in northern areas, replacing conventional medicine.

While the Golden Triangle has long been a centre for opium production and smuggling – it is the world's second-largest opium producer after Afghanistan – yaba production is now spiralling there as well.

Made in isolated factories and labs that can be easily abandoned or dismantled, the drug is mainly created in the forested hills of Shan state in the Burmese corner of the triangle, where policing is minimal and labs difficult to find. Crackdowns have had varying success.

A 2003 war on drugs by the then Thai prime minister, Thaksin Shinawatra, led to more than 2,500 people being killed in three months as police followed orders to act "decisively and without mercy" against suspected dealers.

While popular, the campaign raised questions over just how sure police were that many of those killed were actually involved in the drug trade and by 2011, the authorities estimated that nearly one in 60 Thais was a methamphetamine user.

Just one year later, the public health minister estimated that nearly 7,000 children aged seven to 17 had been rehabilitated for methamphetamine use within the first half of the year alone.

A second crackdown took place between April and June last year, when a joint operation between China, Thailand, Burma and Laos called Mekong Safe seized almost 10 tonnes of drugs, and more than 2,500 suspects were arrested.

But a year on, the trade is far from stemmed. Just last week, police seized 1m yaba tablets stashed in the roof of a pickup truck in Chiang Rai, while in May several people were arrested after 400,000 yaba pills, and 7kg of ice were seized in Bangkok.

Porous borders and corrupt officials mean that the trade requires massive cross-participation from various governments, as well as various and government agencies.

On a recent visit to That Phanom, in Thailand's Nakhon Phanom province bordering Laos, the naval commander of the regional Mekong river patrol unit, Captain Surasak Suwanakesa, told the Guardian that his force regularly intercepted illegal shipments of rosewood, cannabis, yaba and dogs destined for dogmeat in Vietnam and China on the 155 miles of river borders his unit patrolled. But bribes are so common, he added, "you could make millions on this border if you wanted to".

Pushing yaba

Bangladesh is the latest country in Asia to report a surge in use of a methamphetamine pill known as yaba, with research suggesting that criminal syndicates in Burma are targeting users in the country.

The number of methamphetamine pills seized by police each year grew from 36,000 in 2008 to nearly 2 million in 2012, according to Bangladesh's Department of Narcotics Control.

Research by the Jane's Intelligence Review journal suggested that "the trafficking organisation inside Myanmar [Burma] is deliberately providing a promotional rate for exports to Bangladesh".

The surge is reflected in rehab centres in Dhaka. Tarun Kanti Gayen, a clinical psychologist and director of CREA (Centre for Rehabilitation of Drug Addiction), said that until around 2011 80% of clients were heroin addicts, but now yaba users account for up to 70% of the centre's clients. Gayen says it is "drug peddlers or dealers who fuel the demand, they bring yaba and young people rush into it and they get hooked".

Tarique, 24, is a client of CREA in Dhaka, and has been using the drug for 10 years. This is his second spell in rehab; said: "Nowadays everybody is selling yaba, you can find it across the street. Four to five years back it was rare, but now it's dangerous; you can find yaba everywhere." Joseph Allchin, Dhaka