It's cheap, effective and easy to administer - so why are millions of people around the world dying in pain, without access to morphine?
In an open ward at Mulago Hospital in Uganda's capital city, Kampala, an elderly woman named Joyce lies in the fifth bed on the left.
She has twisted the sheets around herself, her face contorted by pain. Joyce's husband, thin and birdlike, hovers over her.
Joyce has cancer - it has spread throughout her body - and until a few days ago, she was on morphine. Then it ran out.
"She's consistently had pain," says a nurse. "And she describes the pain to be deep - kind of into her bones."
The Ugandan government makes and distributes its own morphine for use in hospitals, but poor management means the supply is erratic.
"We're in a very difficult situation," says Lesley Henson, a British pain specialist on duty at Mulago Hospital. They have patients whose pain has been kept under control with morphine - but they are running out it.
In many ways, morphine is an excellent drug for use in developing countries. It is cheap, effective, and simple and easy to administer by mouth.
Yet according to the World Health Organization, every year more than five million people with cancer die in pain, without access to morphine.
"The fact that what stands between them and the relief of that pain is a drug that costs $2 [£1.25] a week, I think is just really unconscionable," says Meg O'Brien, head of The Global Access to Pain Relief Initiative, a non-profit organisation that advocates for greater access to morphine.
O'Brien says in well-off countries, like the UK and United States, there is enough morphine to treat 100% of people in pain - but in low-income countries, it's just 8%.
In many low- and middle-income countries - 150, by some counts - morphine is all but impossible to get. Some governments don't provide it, or strictly limit it, because of concerns that it will be diverted to produce heroin.
And many doctors are reluctant to prescribe morphine, fearing their patients will become addicted.
In India, whether you can get morphine depends largely on where you are treated.
Tata Memorial Hospital, a modern and well-equipped medical centre in Mumbai, has no problem getting morphine for patients.
"We have all the medicines necessary," says Dr Mary Ann Muckaden, head of pain relief at the hospital. "We never run out."
But in other parts of the country, it's a different story. Muckaden estimates only 1% to 2% of Indians with cancer pain get morphine.
Dinesh Kumar Yadav, 28, has come to Tata Memorial - a 30-hour bus ride from his home - to get morphine for his wife.
He tells me she is bedridden with pain but can't get morphine in the north Indian state where they live.
Dr Muckaden says part of the problem is a stifling bureaucracy.
"Many physicians in the north, they don't want to go through the rigorous licensing to store morphine," she explains.
A morphine-use map of the world
- $2 (£1.25) - cost per week per patient
- 100% - percentage of people in UK and US who have access to morphine, if they need it
- 8% - percentage in the developing world who get morphine when required
- 20% of the world's painful deaths are in sub-Saharan Africa, but only 1% of morphine use
There is a place in India where there are no barriers to morphine. But even at the CIPLA Palliative Care Centre in the city of Pune, in Maharashtra state, there are still challenges.
You don't see the challenges when you walk through the cool courtyard gardens with fountains and manicured walkways, or in the beautiful whitewashed buildings with large airy wards, each named after a flower.
"This is heaven on earth," says Asha Dikshit, whose mother came here last year in the last stages of breast cancer.
"She was in agony. Her shoulder had dislocated. It could not be fixed back," says Dikshit. "She had pain in the back, and sometimes there were hallucinations."
But she says her mother died - peacefully - on morphine.
- Comes from the opium poppy
- Discovered in 1804
- First marketed for pain relief in 1817
- Recommended by WHO for pain relief under certain conditions
Every patient here has cancer, and the care is free. The Indian generic drug manufacturer CIPLA supplies the morphine and pays all the other expenses.
But even with all the centre offers, the occupancy rate runs at only about 60%. One big reason, says director Priya Kulkarni, is a result of patients' own concerns about morphine. They often think morphine equals death, and they recoil when doctors suggest it.
Kulkarni says many local oncologists don't want to send patients here for that reason.
"They don't want to give up when it comes to giving them hope," she says. "And saying something like, 'I am going to refer you to a palliative specialist,' is indirectly saying 'There is nothing more I can do for you.'"
Despite all the obstacles to the use of morphine in the developing world, Kulkarni and others say things are starting to move in their direction.
In low-income countries, morphine consumption is up tenfold since 1995, according to the International Narcotics Control Board. And several countries where not many years ago there was no morphine - like Uganda - at least have some today, even if the supply is unreliable.
Back at the hospital in Kampala - where the pharmacy ran out of morphine and Joyce, the cancer patient, had to go without - palliative care specialist Leslie Henson finds a bit of luck. After leaving her patient, she steps into an office, glances at a bookshelf, and sees a forgotten bottle of morphine. It's enough to treat two or three people.
"Hopefully, we'll go take this to her and see what we can do," she says as she troops back to Joyce's room.
Soon, a doctor administers the morphine.
Joyce smiles. Her face untwists. And her husband looks ecstatic.
I ask Joyce if she's glad to get the morphine. Her husband answers. "Very much, indeed."
Other people in the hospital will remain in pain - there is not enough morphine to go around - but for the next few hours, at least, Joyce will be pain-free.