To evaluate the effects of Omega-3 on PMS.

A randomized double blind controlled trial was performed on 184 eligible women. 124 women finally finished the study.

In the case group (n = 70), Omega-3 and in the control group (n = 69) placebo was prescribed.

There were no significant differences between the two groups according to age, BMI, level of education, and the severity and duration of primary symptoms.

45 days after commencing Omega-3, the mean severity of depression (1.85 ± 0.73 vs 3.72 ± 0.65, P = 0.03), anxiety (1.53 ± 1.04 vs 4.07 ± 0.91, P = 0.02), lack of concentration (2. 49 ± 1.26 vs 5.73 ± 1.34 P = 0.03) and bloating (0.95 ± 0.15 vs 2.31 ± 0.19 P = 0.02) in the case group, were all significantly lower than in the control group.

The duration of depression (4.25 ± 1.02 vs 7.21 ± 1.32 days, P = 0.04) and bloating (5.53 ± 2.27 vs 8.33 ± 1.04 days, P = 0.031) in the case group were less than in the control group.

90 days after commencing the treatment, the mean severity of depression (0.95 ± 0.75 vs 3.43 ± 0.65, P = 0.007), anxiety (0.79 ± 1.04 vs 3.89 ± 0.91, P = 0.004), lack of concentration (1.48 ± 1.26 vs 5.63 ± 1.34, P = 0.009), bloating (0.74 ± 0.15 vs 2.14 ± 0.19, P = 0.004), nervousness (2.15 ± 0.93 vs 6.09 ± 0.86, P = 0.01) and the duration of depression (2.12 ± 0.25 vs 7.46 ± 0.02, P = 0.01), nervousness (2.04 ± 0.39 vs 6.33 ± 1.45, P = 0.02), anxiety (4.45 ± 1.02 vs 8.23 ± 1.94, P = 0.03), lack of concentration (2.16 ± 0.26 vs 5.55 ± 1.02, P = 0.02), bloating (3.32 ± 1.01 vs 8.38 ± 2.32, P = 0.004), headache (2.12 ± 0.94 vs 4.28 ± 1.58, P = 0.04) and breast tenderness (4.35 ± 1.31 vs 7.85 ± 2.08, P = 0.02) were lower in the case group.

Omega-3 fatty acids reduces the symptoms of PMS.