Generally, taking tamoxifen does not cause weight gain. If weight gain occurs while taking tamoxifen, it may be caused by taking other drugs, such as hormone drugs. Tamoxifen is used for the treatment of recurrent metastatic breast cancer and is not a hormonal drug, which generally does not directly cause the body to gain weight. If fatness occurs during the medication, it may be caused by other reasons, such as the use of glucocorticoid hormone drugs, suffering from hypothyroidism and so on. Common adverse reactions after tamoxifen medication include gastrointestinal reactions, such as loss of appetite, nausea, vomiting, etc. Adverse reactions such as menstrual disorders, skin rash, etc. may also occur, and there is individual variability in adverse reactions. When fatness or other uncomfortable symptoms occur after taking Tamoxifen, consult a medical professional for consultation.