Some side effects of gabapentin include clumsiness and rolling eye movements that the individual cannot control, says Drugs.com. For children, the side effects include aggressive behavior, crying, depression, hyperactivity, mood swings and restlessness. The child may also be anxious and distrustful and have a delusional sense of well-being. He may have problems concentrating in school.
Less common side effects are black stools with a tarry consistency, pain or swelling in the appendages, painful urination, difficult urination, chest pain and depression or other changes in mood, says Drugs.com. Patients also suffer unusual bleeding or bruising, memory loss, jaundice, nausea and hive-like lesions.
Because gabapentin treats nerve pain and epilepsy, side effects involving the nervous system are common, says Drugs.com. Patients suffer both increased or decreased reflexes, reduced muscle tone, an inability to perform planned actions and involuntary movements. Some of these side effects tend to subside as the patient's body acclimates to the drug.
In a few patients, the side effects are severe, says Drugs.com. They include tumors of the central nervous system, anti-social behavior, subdural hematomas and suicide. A very small percentage of patients develop status epilepticus, which is a type of epilepsy where the patient has nearly nonstop seizures, says MedicineNet. It is a medical emergency.