There is no evidence to show that paracetamol is useful in treating people with cancer pain, either alone or combined with a morphine-like drug. Nor is there evidence to disprove that it is useful. There are no good studies evaluating paracetamol for management of 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. In 1986, the World Health Organization recommended taking morphine-like drugs (opioids) for moderate to severe pain from cancer, and non-opioid drugs like paracetamol, alone for mild to moderate pain, or alongside opioids in people with moderate to severe pain.
In this review we set out to examine all the evidence on how well paracetamol (alone or with morphine-like drugs) worked in adults and children with cancer pain. We also wanted to know how many people had side effects, and how severe those side effects were, for example, whether they caused people to stop taking their medicines.
In March 2017, we found three studies with 122 participants. All compared paracetamol plus opioid with the same dose of opioid alone. The studies were small, and were of poor quality. They used different study designs and different ways of showing their pain results. Outcomes of importance to people with cancer pain were not reported.
We found no evidence that taking paracetamol alone made any difference to the level of pain experienced. We found no evidence that taking paracetamol together with a morphine-like drug was better than the morphine-like drug alone. Paracetamol did not appear to improve quality of life. No conclusions could be reached about side effects. The amount of information and the differences in how studies were reported meant that no conclusions could be made.
Quality of the evidence
The quality of the evidence was very low. Very low-quality evidence means that we are very uncertain about the impact of paracetamol for treating cancer pain. We do not know whether using paracetamol alone, or in combination with an opioid such as codeine or morphine, is worthwhile.
There is no high-quality evidence to support or refute the use of paracetamol alone or in combination with opioids for the first two steps of the three-step WHO cancer pain ladder. It is not clear whether any additional analgesic benefit of paracetamol could be detected in the available studies, in view of the doses of opioids used.
Pain is a common symptom with cancer, and 30% to 50% of all people with cancer will experience moderate to severe pain that can have a major negative impact on their quality of life. Non-opioid drugs are commonly used to treat mild to moderate cancer pain, and are recommended for this purpose in the WHO cancer pain treatment ladder, either alone or in combination with opioids.
A previous Cochrane review that examined the evidence for nonsteroidal anti-inflammatory drugs (NSAIDs) or paracetamol, alone or combined with opioids, for cancer pain was withdrawn in 2015 because it was out of date; the date of the last search was 2005. This review, and another on NSAIDs, updates the evidence.
To assess the efficacy of oral paracetamol (acetaminophen) for cancer pain in adults and children, and the adverse events reported during its use in clinical trials.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and Embase from inception to March 2017, together with reference lists of retrieved papers and reviews, and two online study registries.
We included randomised, double-blind, studies of five days' duration or longer, comparing paracetamol alone with placebo, or paracetamol in combination with an opioid compared with the same dose of the opioid alone, for cancer pain of any intensity. Single-blind and open studies were also eligible for inclusion. The minimum study size was 25 participants per treatment arm at the initial randomisation.
Two review authors independently searched for studies, extracted efficacy and adverse event data, and examined issues of study quality and potential bias. We did not carry out any pooled analyses. We assessed the quality of the evidence using GRADE and created a 'Summary of findings' table.
Three studies in adults satisfied the inclusion criteria, lasting up to one week; 122 participants were randomised initially, and 95 completed treatment. We found no studies in children. One study was parallel-group, and two had a cross-over design. All used paracetamol as an add-on to established treatment with strong opioids (median daily morphine equivalent doses of 60 mg, 70 mg, and 225 mg, with some participants taking several hundred mg of oral morphine equivalents daily). Other non-paracetamol medication included non-steroidal anti-inflammatory drugs (NSAIDs), tricyclic antidepressants, or neuroleptics. All studies were at high risk of bias for incomplete outcome data and small size; none was unequivocally at low risk of bias.
None of the studies reported any of our primary outcomes: participants with pain reduction of at least 50%, and at least 30%, from baseline; participants with pain no worse than mild at the end of the treatment period; participants with Patient Global Impression of Change (PGIC) of much improved or very much improved (or equivalent wording). What pain reports there were indicated no difference between paracetamol and placebo when added to another treatment. There was no convincing evidence of paracetamol being different from placebo with regards to quality of life, use of rescue medication, or participant satisfaction or preference. Measures of harm (serious adverse events, other adverse events, and withdrawal due to lack of efficacy) were inconsistently reported and provided no clear evidence of difference.
Our GRADE assessment of evidence quality was very low for all outcomes, because studies were at high risk of bias from several sources.