Although the rainy season was coming on fast, Zainabu Sesay was in no shape to help her husband. Ditches had to be dug to protect their cassava and peanuts, and their mud hut’s palm roof was sliding off.

But Mrs. Sesay was sick. She had breast cancer in a form that Western doctors rarely see anymore — the tumor had burst through her skin, looking like a putrid head of cauliflower weeping small amounts of blood at its edges.

“It bone! It booonnnne lie de fi-yuh!” she said of the pain — it burns like fire — in Krio, the blended language spoken in this country where British colonizers resettled freed slaves.

No one had directly told her yet, but there was no hope — the cancer was also in her lymph glands and ribs.

Like millions of others in the world’s poorest countries, she is destined to die in pain. She cannot get the drug she needs — one that is cheap, effective, perfectly legal for medical uses under treaties signed by virtually every country, made in large quantities, and has been around since Hippocrates praised its source, the opium poppy. She cannot get morphine.

That is not merely because of her poverty, or that of Sierra Leone. Narcotics incite fear: doctors fear addicting patients, and law enforcement officials fear drug crime. Often, the government elite who can afford medicine for themselves are indifferent to the sufferings of the poor.

The World Health Organization estimates that 4.8 million people a year with moderate to severe cancer pain receive no appropriate treatment. Nor do another 1.4 million with late-stage AIDS. For other causes of lingering pain — burns, car accidents, gunshots, diabetic nerve damage, sickle-cell disease and so on — it issues no estimates but believes that millions go untreated.

Figures gathered by the International Narcotics Control Board, a United Nations agency, make it clear: citizens of rich nations suffer less. Six countries — the United States, Canada, France, Germany, Britain and Australia — consume 79 percent of the world’s morphine, according to a 2005 estimate. The poor and middle-income countries where 80 percent of the world’s people live consumed only about 6 percent.

Some countries imported virtually none. “Even if the president gets cancer pain, he will get no analgesia,” said Willem Scholten, a World Health Organization official who studies the issue.

In 2004, consumption of morphine per person in the United States was about 17,000 times that in Sierra Leone.

At pain conferences, doctors from Africa describe patients whose pain is so bad that they have chosen other remedies: hanging themselves or throwing themselves in front of trucks.

Westerners tend to assume that most people in tropical countries die of malaria, AIDS, worm diseases and unpronounceable ills. But as vaccines, antibiotics and AIDS drugs become more common, more and more are surviving past measles, infections, birth complications and other sources of a quick death. They grow old enough to die slowly of cancer.

About half the six million cancer deaths in the world last year were in poor countries, and most diagnoses were made late, when death was inevitable. But first, there was agony. About 80 percent of all cancer victims suffer severe pain, the W.H.O. estimates, as do half of those dying of AIDS.

Morphine’s raw ingredient — opium — is not in short supply. Poppies are grown for heroin, of course, in Afghanistan and elsewhere. But vast fields for morphine and codeine are also grown in India, Turkey, France, Australia and other countries.

Nor is it expensive, even by the standards of developing nations. One hospice in Uganda, for example, mixes its own liquid morphine so cheaply that a three-week supply costs less than a loaf of bread.

Nonetheless, it is still routinely denied in many poor countries.

“It’s the intense fear of addiction, which is often misunderstood,” said David E. Joranson, director of the Pain Policy Study Group at the University of Wisconsin’s medical school, who has worked to change drugs laws around the world. “Pain relief hasn’t been given as much attention as the war on drugs has.”

Doctors in developing countries, he explained, often have beliefs about narcotics that prevailed in Western medical schools decades ago — that they are inevitably addictive, carry high risks of killing patients and must be used sparingly, even if patients suffer.

Pain experts argue that it is cruel to deny them to the dying and that patients who recover from pain can usually be weaned off. Withdrawal symptoms are inevitable, they say — as they are if a diabetic stops insulin. But the benefits outweigh the risks.