What are the possible side effects of Gabapentin (Gralise, Horizant, Neurontin)?

What are the possible side effects of Gabapentin (Gralise, Horizant, Neurontin)?

Get emergency medical help if you have any of these signs of an allergic reaction: hives; fever; swollen glands; painful sores in or around your eyes or mouth; difficulty breathing; swelling of your face, lips, tongue, or throat.

Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, depression, or if you feel agitated, hostile, restless, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself.

Call your doctor at once if you have a serious side effect such as:

  • increased seizures;
  • fever, swollen glands, body aches, flu symptoms;
  • skin rash, easy bruising or bleeding, severe tingling, numbness, pain, muscle weakness;
  • upper stomach pain, loss of appetite, dark urine, jaundice (yellowing of the skin or eyes);
  • chest pain, irregular heart rhythm, feeling short of breath;
  • confusion, nausea and vomiting, swelling, rapid weight gain, urinating less than usual or not at all;
  • new or worsening cough, fever, trouble breathing; or
  • rapid back and forth movement of your eyes.

Some side effects are more likely in children taking gabapentin.

Contact your doctor if the child taking this medication has any of the following side effects:

  • changes in behavior;
  • memory problems;
  • trouble concentrating; or
  • acting restless, hostile, or aggressive.

Less serious side effects of Neurontin® may include:

  • dizziness, drowsiness, weakness, tired feeling;
  • nausea, diarrhea, constipation;
  • blurred vision;
  • headache;
  • breast swelling;
  • dry mouth; or
  • loss of balance or coordination.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Individual Factors That Also Increase Risk

Several other factors also play a significant role in your likelihood of side effects. Some notable examples include:

  • Genetics: Pharmacogenetics is the name given to the study of how your genes influence your reaction to drugs and genetic factors account for 20-95% of patient variability. This field of pharmacology is rapidly evolving and testing for liver enzyme variations becoming more widespread. For example, codeine requires metabolism through CYP2D6 for conversion to one of its active metabolites, morphine. 5-10% of patients are poor metabolizers – which means that very little codeine is converted to morphine which results in insufficient pain relief. However, 1-2% of people are ultra-rapid metabolizers and more codeine is converted into morphine than normal, resulting in a higher risk of toxic reactions including respiratory depression
  • Kidney function If your kidneys are not functioning at full capacity, then side effects are more likely if you are taking drugs that are excreted through the kidneys. Some other drugs also cease to be effective when kidney function is reduced.
  • Gender: Females have a lower activity of certain hepatic enzymes, a higher body fat to water ratio, and a decreased clearance of drugs through the kidneys than men. Studies have shown the incidence of drug-induced liver toxicity, gastrointestinal side effects, allergic skin reactions, and long QT syndrome is higher in females.

Applies to gabapentin: oral capsule, oral solution, oral suspension, oral tablet

Along with its needed effects, gabapentin (the active ingredient contained in Neurontin) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking gabapentin:

More Common

  • Clumsiness or unsteadiness
  • continuous, uncontrolled, back-and-forth, or rolling eye movements

More common in children

  • Aggressive behavior or other behavior problems
  • anxiety
  • concentration problems and change in school performance
  • crying
  • depression
  • false sense of well-being
  • hyperactivity or increase in body movements
  • rapidly changing moods
  • reacting too quickly, too emotional, or overreacting
  • restlessness
  • suspiciousness or distrust

Less Common

  • Black, tarry stools
  • chest pain
  • chills
  • cough
  • depression, irritability, or other mood or mental changes
  • fever
  • loss of memory
  • pain or swelling in the arms or legs
  • painful or difficult urination
  • shortness of breath
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • swollen glands
  • unusual bleeding or bruising
  • unusual tiredness or weakness

Incidence Not Known

  • Abdominal or stomach pain
  • blistering, peeling, or loosening of the skin
  • clay-colored stools
  • coma
  • confusion
  • convulsions
  • dark urine
  • decreased urine output
  • diarrhea
  • dizziness
  • fast or irregular heartbeat
  • headache
  • increased thirst
  • itching or skin rash
  • joint pain
  • large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs
  • loss of appetite
  • muscle ache or pain
  • nausea
  • red skin lesions, often with a purple center
  • red, irritated eyes
  • unpleasant breath odor
  • vomiting of blood
  • yellow eyes or skin

Some side effects of gabapentin may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More Common

  • Blurred vision
  • cold or flu-like symptoms
  • delusions
  • dementia
  • hoarseness
  • lack or loss of strength
  • lower back or side pain
  • swelling of the hands, feet, or lower legs
  • trembling or shaking

Less Common or Rare

  • Accidental injury
  • appetite increased
  • back pain
  • bloated or full feeling
  • body aches or pain
  • burning, dry, or itching eyes
  • change in vision
  • change in walking and balance
  • clumsiness or unsteadiness
  • congestion
  • constipation
  • cough producing mucus
  • decrease in sexual desire or ability
  • difficulty with breathing
  • dryness of the mouth or throat
  • earache
  • excess air or gas in the stomach or intestines
  • excessive tearing
  • eye discharge
  • feeling faint, dizzy, or lightheadedness
  • feeling of warmth or heat
  • flushed, dry skin
  • flushing or redness of the skin, especially on the face and neck
  • frequent urination
  • fruit-like breath odor
  • impaired vision
  • incoordination
  • increased hunger
  • increased sensitivity to pain
  • increased sensitivity to touch
  • increased thirst
  • indigestion
  • noise in the ears
  • pain, redness, rash, swelling, or bleeding where the skin is rubbed off
  • passing gas
  • redness or swelling in the ear
  • redness, pain, swelling of the eye, eyelid, or inner lining of the eyelid
  • runny nose
  • sneezing
  • sweating
  • tender, swollen glands in the neck
  • tightness in the chest
  • tingling in the hands and feet
  • trouble sleeping
  • trouble swallowing
  • trouble thinking
  • twitching
  • unexplained weight loss
  • voice changes
  • vomiting
  • weakness or loss of strength
  • weight gain

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