Morphine taken by mouth produced good pain relief for most people with moderate or severe cancer pain.
One person in two or three who gets cancer will suffer from pain that becomes moderate or severe in intensity. The pain tends to get worse as the cancer progresses. Morphine taken by mouth has been used since the 1950s for controlling cancer pain. In 1986 the World Health Organization recommended taking an oral solution of morphine every four hours. Morphine is now available in a number of different formats that release the morphine over various periods of time. Morphine Immediate release is rapidly absorbed, and would usually be taken every four hours. Modified release tablets are available that release morphine more slowly, so that they can be taken only twice a day or even only once a day.
In this review we set out to estimate how well morphine worked, how many people had side effects, and how severe those side effects were – for example, whether they were so severe that participants stopped taking their oral morphine. We found 62 studies with 4241 participants. The studies were often small, compared many different preparations, and used different study designs. This made it difficult to work out whether any one tablet or preparation of oral morphine was better than any other. There did not seem to be much difference between them. More than 9 in 10 participants had pain that went from moderate or severe before taking morphine to pain that was no worse than mild pain when taking morphine. More than 6 in 10 participants were very satisfied with the morphine treatment, or considered the result to be very good or excellent. Only about 1 person in 20 stopped taking morphine because of side effects. Morphine is associated with some unwanted effects, mainly constipation, and nausea and vomiting.
At one level these are good results. On another level, we could wish for more consistency in study design, and especially in study reporting, which should include the outcome of pain reduced to tolerable levels – no worse than mild pain – so that people with cancer are not bothered by pain.