Chronic pain cancer patients receiving a strong opioid in combination with paracetamol in a minimum dose of 2 g/day will be randomized to receive either paracetamol in the dose already prescribed (group paracetamol) or an identically looking placebo (group placebo) using the same schedule during the first study phase (days 1-10). In the second study phase (days 11-20) paracetamol or placebo will be stopped in both arms to assess the effect of pill withdrawal on pain control.~Next to baseline the patients will be instructed to use a pain diary to rate their pain during the study and also document the required opioid rescue doses. Further assessments will include adverse events, subjective ratings of quality of sleep, overall feeling of functioning and quality of life. At the screening visit, patients will also be asked to rate their expected changes in pain relief as a result of co-treatment with paracetamol. At the completion of the study, patients will be asked about their preference and whether, overall, they felt their pain was more poorly controlled during the study.~Between the on-site visits at baseline, day 10 and day 20, patients will be followed up by phone calls every 3 days (±1d) and will have an End of Study visit on day 20. Adherence will be checked by pill count and measurement of paracetamol blood concentrations. Genotyping of OPRM1, COMT and relevant CYP enzymes and opioid blood concentrations will be assessed as co-variates for pain control.
Blinded withdrawal of regular co-medication with paracetamol in chronic pain patients under strong opioids on pain control.