OBJECTIVES: I. Evaluate the effectiveness of daily oral pilocarpine versus placebo in relieving dry mouth due to the ongoing use of an opioid for cancer related pain at 2 weeks by comparing proportion of patients with at least one response during the 2 week period, time of first response, and duration of first response. II. Evaluate the adverse effects of pilocarpine in these patients. III. Evaluate whether constipation, sedation, poor appetite, and nausea are ameliorated by pilocarpine in these patients. IV. Evaluate the effect of pilocarpine on quality of life of this patient group. V. Determine the timing and duration of the effect of pilocarpine in this patient population.