Objectives Homeopathic treatment is claimed to be beneficial for primary dysmenorrhoea (PD); still, systematic research evidences remain compromised. This study was undertaken to examine the efficacy of individualized homeopathic medicines (IH) against placebo in the treatment of PD. Methods A double-blind, randomized, placebo-controlled trial was conducted at the gynecology outpatient department of Mahesh Bhattacharyya Homoeopathic Medical College and Hospital, West Bengal, India. Patients were randomized to receive either IH (n=64) or identical-looking placebo (n=64). Primary and secondary outcome measures were 0–10 numeric rating scales (NRS) measuring intensity of pain of dysmenorrhea and verbal multidimensional scoring system (VMSS) respectively; all measured at baseline, and every month, up to 3 months. Group differences and effect sizes (Cohen’s d) were calculated on intention-to-treat (ITT) sample. Results Groups were comparable at baseline (all p>0.05). Attrition rate was 10.9% (IH: 7, placebo: 7). Differences between groups in both pain NRS and VMSS favoured IH over placebo at all time points (all p<0.001, unpaired t-tests and two-ways repeated measures analysis of variance) with medium to large effect sizes. Natrum muriaticum and Pulsatilla nigricans (n=20 each; 15.6%) were the most frequently prescribed medicines. No harms, serious adverse events and intercurrent illnesses were recorded in either of the groups. Conclusions Homeopathic medicines acted significantly better than placebo in the treatment of PD. Independent replication is warranted. Trial registration: CTRI/2018/10/016013.