Objective This study aimed to determine the efficacy of probiotic gargles compared with placebo gargles on reducing post-tonsillectomy morbidity in adults. Method This was a triple-blind, randomised, controlled trial and feasibility study. Thirty adults underwent elective tonsillectomy and were randomly assigned to receive either probiotic or placebo gargles for 14 days after surgery. Daily pain scores and requirement of analgesia were measured for 14 days post-operatively. Secondary outcomes assessed probiotic safety and tolerability and the feasibility of the trial. Results The probiotic group experienced less pain at rest on day 2. However, the amount of oxycodone (5 mg) tablets used was greater in the probiotic group compared with placebo. There were no statistically significant differences in the frequency of adverse effects between both groups. This trial was feasible. Conclusion This pilot study suggested that probiotic gargles do not reduce post-tonsillectomy pain or bleeding, highlighting the importance of pilot and feasibility studies in clinical research.