Doxycycline is a highly-efficient medication often prescribed for the treatment of infections caused by the multiplication of bacteria. These include respiratory tract infections, urinary tract infections, acne, infections of the skin, as well as pneumonia and Lyme disease. Doxycycline has been reported to cause harm to unborn babies. If you are taking this medicine and you think you may have become pregnant talk to your health care provider as soon as possible. If you notice any of the following side effects of doxycycline you can continue the treatment but make sure they do not get worse over time: sores inside your mouth, vaginal itching, stomach upset, diarrhea, vomiting, vaginal discharge, swollen tongue, mild nausea, trouble swallowing, swelling in the rectal or genital area. These side effects are short-lived and mild, but if they get worse call your health care professional that prescribed doxycycline. If there are any risks associated with your treatment, due to health problems or taking any other medications simultaneously with doxycycline, your condition will be monitored by a qualified health care professional. However, you also need to watch for some symptoms that appear serious and can cause health complications, including any of the following ones that must be reported immediately as you notice them: stomach pain, loss of appetite, hives, upset stomach, extreme weakness, itching, yellowing of the skin or eyes, dark-colored urine, confusion, vomiting, skin rash, severe headache, and blurred vision.