Possible side effects of doxycycline include tenderness in the stomach or abdomen, bloating, a rapid heartbeat and a loss of appetite, according to Drugs.com. Other possible side effects include feeling uncomfortable, fever, headache and inflamed joints. Some people may pass black, tarry or clay-colored stools after taking doxycycline.
Doxycycline may cause some people to pass diarrhea, which may or may not be bloody, as well as dark urine, states Drugs.com. Some people may have difficulty swallowing after taking doxycycline. Doxycycline may cause the feet, hand or feet to become numb or tingly. It can also cause hives or swelling on the hands, legs, throat or feet. Hive-like swelling may also occur on the eyelids, lips, tongue or sex organs.
Doxycycline can cause unusual weight loss, notes Drugs.com. Some people may experience swollen lymph glands, mouth sores, redness of the skin or soreness or redness of the eyes. The drug can cause jaundice, which is the yellowing of the eyes or skin. Some people may feel exceptionally thirsty after taking doxycycline. It may cause a rash or welts.
It is important to check with a physician if any of these or other side effects occur, recommends Drugs.com. Some side effects may subside naturally over time as the body gets used to the medication.