Hello I have gone through your question and understood your concern. PROSTAP injections are used to reduce the levels of testosterone and estrogen circulating in the body and it is indicated to treat prostate cancer in men and endometriosis and uterine fibroids in women. -There is not interaction between your prostap injections and levothyroxine(the thyroid hormone replacement therapy).The injections do not interfere with thyroid,don t worry! Anyway my advice is to take Levothyroxine on an empty stomach, at least 30 minutes before breakfast and to follow your treating doctor s dosing instructions. Second advice:It is better if you avoid the injections within 4 hours before or 4 hours after you take levothyroxine. You have some symptoms that can be suggestive of hypothyroidism like tiredness,low heart rate,dizziness.For this reason,if you were my patient i will ask to do the TSH test because you may need to increase the dosis of levothyroxine. At the other side,You re losing weight(more than 5% of your weight within short periods of time)without trying and you re not sure why. My advice is to contact your treating doctor and discuss with him about this important symptom and the possible causes. Meantime Eat more often,choice healthy hypercaloric foods,use bigger plates,don t drink water before meals and get quality sleep. Hope this is helpful. If you have other doubts,feel free and ask. Regards.