Diarrhea, loss of appetite, nausea, vomiting, headache, dizziness, lightheadedness, or rectal discomfort may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including: darkening of the skin and other areas of the body (such as lips, inside of the mouth), difficult/painful swallowing, unusual increase in the amount of urine (except for the expected increase in urination if you are treating SIADH), unusual decrease in the amount of urine or no urine, unusual thirst, weakness, unusual tiredness, brown/gray tooth discoloration, hearing changes (such as ringing in the ears, decreased hearing), easy bruising/bleeding, new signs of infection (such as sore throat that doesn't go away, fever, chills), signs of liver disease (such as nausea/vomiting that doesn't stop, stomach/abdominal pain, yellowing eyes/skin, dark urine).

Tetracycline drugs such as demeclocycline may rarely cause increased pressure around the brain (intracranial hypertension-IH). The risk of this side effect is greater for women of childbearing age who are overweight or who have had IH in the past. If IH develops, it usually goes away after demeclocycline is stopped; however, there is a chance of permanent vision loss or blindness. Get medical help right away if you have: nausea/vomiting that doesn't stop, headache that is severe or doesn't go away, vision changes (such as blurred/double vision, decreased vision, sudden blindness).

This medication may rarely cause a severe intestinal condition due to a bacteria called C. difficile. This condition may occur during treatment or weeks to months after treatment has stopped. Tell your doctor right away if you develop: diarrhea that doesn't stop, abdominal or stomach pain/cramping, blood/mucus in your stool.

If you have these symptoms, do not use anti-diarrhea or opioid products because they may make symptoms worse.

Use of this medication for prolonged or repeated periods may result in oral thrush or a new vaginal yeast infection. Contact your doctor if you notice white patches in your mouth, a change in vaginal discharge, or other new symptoms.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, skin sores/blisters, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing, new or worsening swelling/pain in the joints, chest pain, fast/irregular heartbeat.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.