Complex sentence: Most research indicates that orally-administered evening primrose oil does not relieve symptoms of premenstrual syndrome, neither does orally administered primrose oil seem to have any effect in shortening the length of pregnancy or labour.
Split into simpler sentences: Most research indicates that orally-administered evening primrose oil does not relieve symptoms of premenstrual syndrome. Neither does orally administered primrose oil seem to have any effect in shortening the length of pregnancy or labour.