Bactrim (co-trimoxazole) can be prescribed for the treatment of infections that affect your ears, urinary tract, eyes, ears and other organs. Bactrim may sometimes cause an upset stomach - make sure you always take this medicine with some food if you think there may be chance you will get upset stomach when using this medicine. Some other side effects are also possible but they are unlikely to last for to long or get bothersome over time. Tell your health care provider if at the beginning of your treatment you get spinning sensation, loss of appetite, vomiting, dizziness, upset stomach, sleep problems, joint pain, or swollen tongue. Those mild side effects may need to be monitored, but do not need to be treated in any way. It's very important to take the entire amount of Bactrim prescribed, as otherwise you are not going to benefit from the treatment. If you stop taking Bactrim suddenly, a relapse of infections is possible. Do not combine it with seizure medications, methotrexate, ACE inhibitors, diuretics, or blood thinners, as interactions have been reported. Always ask your doctor any questions you may have instead of acting without thinking about it properly.