Pain at the injection site may occur. If this effect lasts or gets 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: joint/muscle pain, severe pain/peeling skin at injection site, numbness/tingling of arms/legs, pain/redness/swelling of arms or legs, change in skin color near injection site or on arms/legs, uncontrolled movements, inability to move, signs of kidney problems (such as change in the amount of urine), new signs of infection (such as sore throat that doesn't go away, fever), easy bruising/bleeding, dark/cloudy urine, seizures, mental/mood changes (such as depression, agitation).

Get medical help right away if you have any serious side effects, including: chest pain, trouble speaking, vision changes, fainting.

This medication has rarely caused a very serious (possibly fatal) blood disorder (methemoglobinemia). This effect is more likely if you have breathing problems, certain diseases of the blood, or if you smoke (see also Precautions section). The symptoms of this disorder may occur within minutes to a couple of hours after using this medication. Stop using this medication and get medical help right away if you develop any symptoms of methemoglobinemia, including: headache, confusion, dizziness, shortness of breath, tiredness, pale/bluish/gray skin, fast heartbeat.

If used to treat syphilis, this medication may cause a condition known as Jarisch-Herxheimer reaction. This condition may occur 1 to 2 hours after you receive the medication and can last up to 24 hours. Notify your doctor right away if you experience any of these symptoms: fever/chills, muscle pain, worsening of skin sores, fast heartbeat, fast breathing, dizziness, flushing.

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, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

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.