The aim of this study is to compare the efficacy provided by spirulina platensis and cetirizine for treatment of allergic rhinitis (AR). A randomised controlled clinical trial was performed on 53 patients with AR divided into experimental and control groups in an accredited tertiary academic centre. Subjects in the experimental group were treated with spirulina (2 g per day) and the control group was treated with cetirizine (10 mg per day) for 2 months. Symptoms were assessed based on a standard questionnaire and inflammatory mediators, and the results were compared before and after treatment. There were 23 men and 30 women with a mean age of 26.75 years (SD 9.26; range 8-58). The differences between the two groups in terms of age and gender were not significant. There was no significant difference between the two groups in clinical presentations before the intervention (P > 0.05). The prevalence of rhinorrhoea (P = 0.021), nasal obstruction (P = 0.039) and smell reduction (P = 0.030) in the experimental group improved significantly compared to those seen in the control group after intervention. Sleep condition, daily working and social activity improved significantly in the experimental group (P < 0.05). Furthermore, there was no significant difference between groups regarding inflammatory mediators before treatment; however, after 1 month of treatment, the levels of interleukin (IL)-1α (P < 0.001), IL-1β (P < 0.001) and IL-4 (P = 0.008) were all significantly lower, and IL-10 levels were significantly higher in the experimental group, compared to those in the control group. In conclusion, spirulina is more effective than cetirizine in improving cardinal symptoms of AR patients. Furthermore, spirulina can be considered as an alternative treatment in patients with AR.