However, even as the reach of the painkiller widens, China faces ever greater challenges in managing the use of inherently risky opioids within its sprawling, state-run health care system.

Several doctor training presentations in a government-backed pain-management campaign, for which Mundipharma provides organisational support, as well as some on the company’s online platforms, highlight decades-old foreign studies that downplay the risks of opioid addiction.

The programmes reach tens of thousands of local doctors, often familiarising them with the purported superiority of OxyContin.

While Mundipharma said it did not prepare the materials itself, the company appears to have benefited from its involvement in the health ministry’s pain management programme.

Studies on prescription data show that OxyContin sales rose sharply in several Chinese hospitals when they implemented the programme.

Mundipharma claims a 60 per cent share of the China market for cancer pain therapies, according to an interview with its China head posted on its website.

The World Health Organisation recommends strong opioids for cancer pain when lesser alternatives are ineffective, while saying that doctors should also be alert to possible adverse effects.

“Certainly doctors and patients should be aware if they use strong opioids that there is small but significant risk of developing a dependence to those opioids,” said Nicolas Clark, a Switzerland medical officer in the WHO’s mental health and substance abuse department.

“If the cancer is cured or the patient’s life expectancy is good, this opioid dependence may require separate treatment.”

Mundipharma China said in an e-mailed statement that it had rigorous internal policies to ensure that it complied with Chinese laws, and worked responsibly to improve pain management.

The company said the training materials in the government campaign had been prepared by experts commissioned by China’s Ministry of Health.

China’s National Health and Family Planning Commission, which the health ministry was merged into 2013, did not respond to requests for comment.

Worldwide, the market for opioids – a wide range of compounds extracted from opium poppies or artificially altered or synthesised – rose about 3 per cent to US$35 billion in 2015, according to a report by consultancy Persistence Market Research.

With its 4.3 million new cancer patients last year, China may offer the most lucrative expansion possibilities.

There are also other factors at play: China’s low rates of opioid consumption suggest many patients are under-treated for severe pain. Demand for drugs such as OxyContin is also rising as Chinese attitudes toward end-of-life care, once a taboo subject, have evolved.

Unlike the US, China does not have an addiction outbreak even though demand for painkillers has risen. But as the Asian country widens opioid use, the training of doctors will be key to ensuring they are prescribed appropriately, and to preventing diversion and abuse.

Mundipharma, whose China portfolio is dominated by pain treatments, had about US$100 million in overall China sales last year, a 45 per cent increase over 2014, according to an earlier Bloomberg Businessweek interview with its Asia president. The company did not disclose the percentage of sales that came from OxyContin.

Mundipharma’s work with China’s government goes back to 2011, when it began to assist the Good Pain Management programme, organised by the health ministry and implemented by the Chinese Society of Clinical Oncology, an academic association.

The company said that its “support for the Good Pain Management programme covers activities such as coordinating venues and providing organisational support at the sessions themselves”.

The literal English translation of the health ministry’s campaign is “standardised cancer pain treatment”.

One specialist at a top hospital in Beijing said he and his colleagues had joked that what they saw as the programme’s emphasis on OxyContin would be similar to making Kung Pao Chicken the only “standardised” dish to be eaten at every meal.

Despite potential benefits and the Chinese government’s backing, patients need to be open-eyed about what oral opioids such as OxyContin can accomplish, some doctors say.

In April, Jiang Chuying, a 41-year-old textile worker and cancer patient, first took a 10 milligram OxyContin tablet, for leg and back pain. By late July, she was consuming 60 pills daily – each at four times the initial strength.

“She was almost taking those pills instead of food,” said her younger sister Jiang Xueying, who was Chuying’s main caregiver after she was diagnosed with colorectal cancer in August last year. “I asked the doctor why the painkiller couldn’t stop the pain. The doctor said you can only keep adding.”

As Chuying travelled to six hospitals over the course of her treatment, she was prescribed rapidly rising doses of OxyContin, but the one-track approach did not work. During her inpatient stays “the entire floor of the ward could hear her screaming in pain”, Xueying said.

One of the doctors who treated Chuying in her final months, who asked to be identified only by his surname, Huang because he did not have permission from his hospital to comment, said he suspected Chuying might have been suffering from neuropathic pain and wasn’t sure OxyContin was the best course of treatment.

Huang said he had been told a follow-up inspection from the pain management campaign was due at his hospital and he was reluctant to try alternative treatments. The inspection was later cancelled and Huang ultimately shifted to ketamine, a non-opioid anaesthetic.

Chuying’s pain levels fell from moderate to mild before she died in August, according to her medical records.

The World Health Organisation recommends that some opioid medicine be used for cancer pain, although it is not recommending OxyContin specifically.

“There’s no evidence that oxycodone is more effective than other strong opioids,” said Clark, referring to the drug’s generic name.

OxyContin is a long-acting oxycodone tablet, and according to the Chinese drug regulator’s database, the only such product sold in China.

Alternative opioids in the country include oral morphine, a type of skin patch and various injectable formulations.

Slides used in a training session for the government’s campaign in eastern Zhejiang province, viewed by Bloomberg News, highlighted OxyContin as a global bestseller that can alleviate various kinds of cancer pain with few side effects. The slides then devoted several pages to the shortcomings of rival therapies.

Citing two Western studies, they also showed data indicating about 0.03 per cent addiction rates among patients taking opioids to manage pain. Virtually identical content was shown at a pain conference in Beijing.

Both presentations cited a letter by Jane Porter and Hershel Jick published, in the New England Journal of Medicine in 1980, and another 1990 study that said opioids have low addiction risks.

A patient education manual carried on the website of Mundipharma China, also cited the Porter and Jick study, saying that addictions were extremely rare when opioid drugs were taken to treat pain. Some videos from Mundipharma’s Class Room on Air training programme referenced data finding only seven addictions in every 24,000 patients.

Outside experts said such studies were dated and misleading. “That’s a gross underestimation of the situation we see today. The rate of addiction is closer to 10 per cent, and of misuse in the range of 20-30 per cent,” said Clark, regarding addiction rates in non-cancer patients.

While the rates of misuse in cancer pain were likely to be lower, cancer patients could also be at risk, he said, and one recent study he pointed to in a palliative-care clinic found 15 per cent of patients exhibited opioid use disorders.

Mundipharma China said the Class Room on Air presentations were prepared by speakers, and the manual posted on its website was owned by the Chinese Society of Clinical Oncology.

The company said it was not involved in preparing those or the government campaign materials, and Bloomberg could not independently ascertain their origins. The head of the oncology society could not be reached.

Wang Xiaojia, an oncologist at Zhejiang Cancer Hospital, who has given lectures to physicians for the campaign, and whose name appeared on one of the presentations reviewed by Bloomberg, could not recall where the materials originated from.

He did not prepare them himself, he said. Content for such small lectures was often provided by the pharmaceutical company inviting the speaker, he said, adding he often deviated from slides to what he thought the audience needed to learn.

In the US, prescribed opioid drugs have become widely used to treat non-cancer pain since the 1990s, and 1.7 million Americans used OxyContin “non-medically” in 2015, such as without prescriptions, according to a report earlier this year from the US Department of Health and Human Services.

In 2007, Purdue Pharma and three current and former company executives pleaded guilty and agreed to pay US$634.5 million to settle criminal and civil claims that they misled doctors as to the addictiveness of OxyContin.

Purdue said via e-mail that it had accepted full responsibility for the actions some of its employees took prior to 2002.

Purdue, which is not responsible for China sales, said that in the US it has taken steps, including developing medications with abuse-deterrent properties and supporting monitoring programmes. It did not respond to requests to make a Sackler representative available for comment.

China has stricter rules of opioid use than the US. The Chinese drug regulator, among other things, mandates that patients who do not have only cancer, be given opioids when other pain relief methods have failed, they are above 40 years of age and have suffered for more than four weeks. Doctors are also required to get narcotics training before getting rights to prescribe them.

Medical workers from 6,200 hospitals across the country paid 64,000 visits to online lectures hosted by Mundipharma’s platform to promote pain treatment and the company plans a broader outreach to primary care doctors over the next three years, according to its website.

Wang agreed that Mundipharma was getting a sales boost from the government’s pain management campaign.

“Of course, that exists,” he said. Wang said the government guidelines included a wide range of treatment options, and some physicians may have misunderstood the campaign’s message if they thought OxyContin was specifically recommended.

At least 10 studies on prescriptions at individual hospitals published in Chinese medical journals demonstrate direct links between the government campaign and significant increase in the use of OxyContin.

For example, a hospital in the northwestern Xinjiang region used no OyxContin before it took part in the campaign in 2014. By March 2015, the drug had become its most used cancer pain treatment, accounting for 98 per cent of the expense on cancer pain drugs.

While in China OxyContin is used mainly for cancer pain, it is also approved for other types of chronic pain, such as in the joints and back.

A recent search on Chinese online forums showed many posts offering to resell or give away leftover OxyContin from family members who had passed away.

When Chuying died, she left behind 101 of boxes of OxyContin that she had been prescribed for home use after leaving the hospital.

The doses wrapped in plastic, are now sitting in a corner of the house of her sister Xueying, who is unsure how to dispose of the 1,010 pills.