For example, an excessive amount of morphine given to lung cancer patients can lead to respiratory problems. Fearful an overpresciption of narcotics could hasten death, doctors may decide it is better to leave the patient to deal with his illness.
A study last year found one in four elderly cancer patients in nursing homes received no treatment for daily pain.
However, that trend is starting to change. At least 15 states recently have passed laws ensuring doctors' licenses won't be revoked for prescribing powerful controlled substances like morphine for severe pain.
The organization that accredits hospitals approved standards in August declaring that all patients have a right to proper pain management.
And last month, Oregon's medical board became the first to ever discipline a doctor for undertreating pain. Among the complaints was that the doctor only provided Tylenol for a dying cancer patient's pain.
But some doctors fear that legislation pending in Congress could reverse that progress.
The controversial legislation would formally declare prescribing controlled substances to alleviate pain a legitimate medical decision even if those drugs increase risk of death. Pain experts praise the protection as a crucial step to improve patient care.
But that same bill, the Pain Relief Promotion Act, also enters a minefield, by banning controlled substances for the purpose of physician-assisted suicide. Take strong steps to control pain, the bill says, but don't intentionally hasten death.
Today, assisted suicide is legal in only one state, Oregon. The federal legislation would essentially overturn Oregon's state law. Many in Oregon say Congress should not, as Sen. Ron Wyden, D-Ore., put it, "throw the votes of our citizens in the trash can." The bill's author, Sen. Don Nickles, R-Okla., counters that the issue is no different than Congress intervening if a state legalized heroin.
But the Oregon fight aside, some physicians including those opposed to assisted suicide raise a bigger health concern: That judging whether prescribing decisions are proper or improper could cause a backlash against pain treatment.
The average doctor might say, "I should use less controlled substances," worries pain expert Dr. James Rathmell of the University of Vermont. "That's not what the legislation is intended to do at all, but how do we prevent it?"
One key, Rathmell told a Senate committee this week, is proper training and oversight of the federal officials who would enforce the law.
Lawmakers are struggling with how to ensure that balance. The issue is "one of the most difficult subjects this committee has ever dealt with," said Sen. James Jeffords, R-Vt. A version of the bill has passe a key House committee, but Jeffords' Senate health committee is unlikely to have time to vote on the issue this year.
Regardless, the controversy is raising public awareness of proper pain treatment.
For the vast majority of terminally ill patients, pain can be controlled.
"I would plead for better pain control," Rathmell advised. "Focus their physician's attention on pain being the issue, not preservation of life."
Specialists like Rathmell can advise doctors without extensive training in pain treatment. As for that other excuse doctors sometimes use that narcotics are addictive, research shows that's not a big issue when treating intractable pain, especially if someone is weeks or months from death.
Rathmell recalled his lung cancer patient: "To see a peaceful death, which is what we're all looking for it would be a shame not to have helped with that when we know we could."