Objective: To investigate the effects of 3-month supplementation with oral probiotics on quality of life in young women with primary dysmenorrhoea Design Randomized, double blind, placebo-controlled trial Setting A tertiary university hospital in Malaysia Population Women aged 18 to 45 years old suffering from primary dysmenorrhoea Methods: 72 patients were randomized to receive either oral sachets containing Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus lactis, Bifidobacterium bifidum, Bifidobacterium longum, and Bifidobacterium infantis 107 mg each or placebo twice daily for three months. Main outcome measures Visual Analog Score (VAS) of pain, Verbal Rating Scale (VRS) of severity, frequency of non-steroidal anti-inflammatory drugs (NSAIDs) use, and quality of life (QoL) scores derived from Short Form 12 item version 2 (SF12v2) questionnaire Results Both groups showed improvement in quality of life scores. There was a non-statistically significant lower NSAIDs use in probiotic group compared to placebo group (median 1 vs 2, p-value = 0.26). Placebo group showed better severity score (VRS) on day 2 of menses compared to probiotic group (median 0 vs 1, p-value <0.05). No difference in other quality of life scores was noted. In subgroup of non-NSAIDs users, the pain score (VAS) was lower in the probiotic group compared to placebo, which was not statistically significant (p-value = 0.59) Conclusion Probiotic supplement may reduce NSAIDs use in women with primary dysmenorrhoea Funding This study receives supply of the oral probiotic sachets and placebo from the manufacturing company Hexbio Sdn Bhd Keywords Primary dysmenorrhea, probiotics, quality of life, menstrual disorders