Hello, Yes, if taken together they may cause harmful interactions. Euthyroxine, Progynova and Duphastan may interfere with blood glucose control and reduce the effectiveness of Metformin. You need to monitor your blood sugar levels closely and also a dose adjustment of Metformin during and after treatment with Progynova and Duphastan. Beside before taking Progynova you may need dose adjustments of Euthyrox or thyroid function tests in order to safely take both medications together. You should notify your doctor if you have symptoms of low thyroid such as tiredness, feeling cold, constipation, unexplained weight gain, depression, joint or muscle pain, thinning hair or hair loss, dry skin, hoarseness, and abnormal menstrual periods. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Mohammed Taher Ali