The generic tamoxifen drug can have various side effects. If you show symptoms of an allergic reaction to tamoxifen, such as hives, swelling in the throat, mouth or face, or difficulty breathing, seek immediate medical attention. Serious side effects of tamoxifen include: new breast lumps; headaches, confusion, vision or balance problems; sudden weakness or numbness; pain or swelling in either one leg or both; irregular menstruation; nausea, stomach pain, fever, jaundice, dark urine or clay-colored stools; or more. If any of these symptoms arise, inform your local physician at once. Before you buy tamoxifen online, talk with your local doctor about your risk factors of side effects. Other, less-serious side effects can include: a cough or sore throat; irritability or agitation; depression or weakness; nausea; weight loss; hot flashes; and more. Other side effects may occur, whether you think these may be caused by tamoxifen or another drug inform your local doctor.