Get emergency medical help if you have signs of an allergic reaction to Horizant: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, upper stomach pain, or yellowing of your skin or eyes. This reaction may occur several weeks after you began using Horizant.
Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), depressed, or have thoughts about suicide or hurting yourself.
Call your doctor at once if you have:
weak or shallow breathing;
blue-colored skin, lips, fingers, and toes;
confusion, extreme drowsiness or weakness;
problems with balance or muscle movement;
unusual or involuntary eye movements; or
increased seizures.
Gabapentin can cause life-threatening breathing problems. A person caring for you should seek emergency medical attention if you have slow breathing with long pauses, blue colored lips, or if you are hard to wake up. Breathing problems may be more likely in older adults or in people with COPD.
Some side effects are more likely in children taking gabapentin. Contact your doctor if the child taking this medicine has any of the following side effects:
changes in behavior;
memory problems;
trouble concentrating; or
acting restless, hostile, or aggressive.
Common Horizant side effects may include:
headache;
dizziness, drowsiness, tiredness;
problems with balance or eye movements; or
(in children) fever, nausea, vomiting.
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.
 Horizant side effects (more detail)
