If you are taking amoxicillin with clarithromycin and/or lansoprazole to treat stomach ulcer, use all of your medications as directed. Be sure to read the medication guide or patient instructions provided with each of your medications. Do not change your doses or medication schedule without advice from your doctor. You may take amoxicillin with or without food. If you are being treated for gonorrhea, your doctor may also have you tested for syphilis, another sexually transmitted disease. Do not give amoxicillin to another person, even if they have the same symptoms you do. Amoxicillin can cause you to have unusual results with certain medical tests. Tell any doctor who treats you that you are using amoxicillin.