Hi, Cortisone injections can affect the menstrual cycle, but it is not a common side effect. Delayed periods and changes in menstrual flow can be caused by a variety of factors, including stress, changes in diet or exercise, weight fluctuations, hormonal imbalances, and certain medications. It is also possible that the injections have nothing to do with your menstrual changes, and that they are just a coincidence. About your light flow of dark blood, I can confidently say that it s usually just old blood that s lingered in your body too long. This could occur at the beginning or ending of the menstruation when the flow is low. It is important to talk to your doctor about any changes in your menstrual cycle, especially if you have a history of PMDD. Your doctor may recommend further testing or evaluation to rule out any underlying medical conditions. They may also be able to offer advice on how to manage your PMDD symptoms during this time. In the meantime, it may be helpful to track your menstrual cycle and any associated symptoms to see if there are any patterns or trends. You can use a menstrual cycle tracking app or calendar to help with this. Additionally, taking steps to manage stress, eat a balanced diet, and get regular exercise may help regulate your menstrual cycle and improve your overall health. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zia Ul Haq, General & Family Physician