Abstract Background There is considerable interest in improving the scoring methods for evaluating the efficacy of allergen immunotherapy (AIT) and to show if this is associated with clinically meaningful results from the patient's perspective. We aimed to assess the efficacy and clinical relevance of a 300 index of reactivity (IR) 5‐grass pollen sublingual immunotherapy (SLIT) tablet in children, adolescents and adults with moderate to severe grass‐induced allergic rhinoconjunctivitis (ARC) with or without controlled asthma using the combined symptom and medication score CSMS0‐36. Methods The data of the European population that participated in 3 Phase III, international, randomized double‐blind placebo‐controlled clinical trials were analyzed post hoc. Results A total of 864 patients randomized to 300 IR 5‐grass tablet or placebo were analyzed. Over the primary evaluation period, the difference in CSMS0‐36 between the 300 IR and placebo groups was statistically significant (point estimates: −2.51, CI95% [−3.88; −1.14], p