Based on the research studies that have been done, the Medical experts at Lindora do not believe the evidence suggests that this is helpful for weight loss.
There have been some good studies to evaluate the effects of primrose oil as a weight loss aid and, based on these, we can not recommend it.
A double-blind evaluation of evening primrose oil as an anti-obesity agent. Haslett C, Douglas JG, Chalmers SR, Weighhill A, Munro JF
Evening Primrose Oil (EPO) is a naturally occurring rich source of essential fatty acids, especially linoleic and gamma-linolenic acid. It has been suggested that it has anti-obesity properties. One double-blind 12-week study was undertaken in 100 women with substantial obesity: 40 with long-term obesity, and 60 at time of their first referral to a clinic. Seventy-four subjects completed the study. Those treated with EPO were comparable in age and degree of obesity with the placebo-treated group. There was no significant difference in the weight loss achieved by those taking EPO compared with placebo, either in the subjects with refractory obesity or in those treated at time of initial referral. It would appear that any anti-obesity property possessed by EPO is clinically insignificant.  Parallel placebo-controlled clinical study of a mixture of herbs sold as a remedy for cellulite. Lis-Balchin M Cellasene, a product containing Ginkgo biloba, sweet clover, sea-weed, grape seed oil, lecithins and evening primrose oil, has been marketed all over the world as a miracle cure for cellulite. As the efficacy of the product was in doubt, a parallel placebo-controlled clinical study was undertaken in a group of women to see whether the product had any effect on cellulite, or on the body weight, fat content, circumference of thighs, hips, etc. No significant changes were found in these parameters compared with the starting values, nor compared with the placebo control after a 2 month course of Cellasene, except for an increase in the cellulite, assessed by the author, compared with that initially.
Seven of 11 women taking Cellasene gained weight, as did eight in the placebo control group, taking Colonease. The weight gain in both groups was apparent after the first 2 weeks, and all women had to reduce their food consumption. Only three of the women in the Cellasene group thought that their cellulite had slightly improved against two women in the control group. [1.] Int J Obes 1983;7(6):549-53 [2.] Phytother Res 1999 Nov;13(7):627-9