 The most commonly reported medication-related adverse reactions in people taking dydrogesterone without an estrogen in clinical trials of indications have included menstrual irregularities, headaches, migraines, nausea, breast tenderness, bloating, and weight gain.The use of progestins, in particular medroxyprogesterone acetate, in treating postmenopausal symptoms have been associated with increased risk of blood clots and breast cancer in a study carried out by the Women's Health Initiative.While the study did not involve dydrogesterone, it is possible, but not certain, that it too increases these risks.