Oxcarbazepine, sold under the brand name Trileptal, causes side effects in most people who take it. Dizziness is the most common, affecting about 30% of patients in clinical trials. Most side effects are related to the nervous system and tend to improve as your body adjusts to the medication, but some require monitoring and a few are rare but serious.
The Most Common Side Effects
In clinical trials, the side effects that showed up most often were neurological. Dizziness topped the list at roughly 30% of patients, compared to about 15% of those taking a placebo. Sleepiness affected around 13%, and headaches occurred in about 12%. Double vision was also notably common at 11%, a side effect that catches many people off guard since they don’t expect a seizure medication to affect their eyes. Blurred vision occurred less frequently, in about 2 to 4% of patients.
Stomach-related side effects were also common. Nausea hit about 12% of patients, and vomiting affected around 11%. These numbers were fairly close to what placebo groups experienced, which means some of the nausea people feel may not be entirely caused by the drug itself.
Fatigue and general weakness each affected roughly 5% of patients. Some people describe this as feeling physically drained or lacking their usual energy, particularly in the first weeks of treatment.
Side Effects Increase With Higher Doses
Oxcarbazepine’s side effects are clearly dose-dependent. In trials comparing a higher dose (2,400 mg/day) to a lower dose (1,200 mg/day), the differences were striking. Dizziness jumped from about 20% at the lower dose to 41% at the higher dose. Vomiting went from 6% to 15%. Double vision climbed from 10% to 13%. This pattern held across nearly every side effect category.
This is why doctors typically start at a low dose and increase gradually. The goal is to find the lowest effective dose, which limits side effects. Many of the neurological side effects that appear early on, like dizziness and coordination problems, tend to improve over time as your body adjusts, even without reducing the dose.
Thinking and Coordination Problems
The FDA specifically warns about three categories of brain-related side effects: cognitive symptoms, sleepiness, and coordination problems. Cognitive effects include slower thinking, difficulty concentrating, and trouble finding words or speaking clearly. These aren’t subtle for everyone. In some cases, people notice they’re fumbling through conversations or struggling to focus at work.
Coordination problems, including unsteady walking and poor balance, affect roughly 10 to 13% of patients. In children, these numbers are similar. Pediatric trials found that 13% of children on oxcarbazepine experienced coordination difficulties compared to 4% on placebo, and 31% experienced sleepiness compared to 13% on placebo. Children between ages 2 and 4 appear to be the most affected age group for these symptoms.
Low Sodium Levels
One of the more medically significant side effects is hyponatremia, a drop in blood sodium levels. Clinically significant cases (where sodium falls below 125 mmol/L) occur in about 2.8% of patients. That may sound small, but low sodium can cause confusion, nausea, headaches, seizures, and in severe cases, it can be dangerous.
The risk is higher if you’re older, taking multiple seizure medications, or using diuretics (water pills). Your doctor will likely order periodic blood tests to check your sodium, especially during the first few months. Symptoms of low sodium can mimic the drug’s other side effects, so it’s easy to miss without a blood test.
Bone Health Over Time
Long-term use of oxcarbazepine can weaken bones. A meta-analysis found that oxcarbazepine significantly reduces bone mineral density in children. The mechanism involves the drug speeding up the breakdown of vitamin D in the liver, which leads to lower vitamin D levels, a compensatory rise in parathyroid hormone, and ultimately weaker bones.
Studies confirmed that children on oxcarbazepine had measurably lower vitamin D levels and higher parathyroid hormone. If you or your child will be on this medication long-term, it’s worth discussing bone density monitoring and vitamin D supplementation with your doctor.
Serious Allergic and Skin Reactions
Rare but potentially life-threatening skin reactions can occur, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). These conditions cause widespread skin blistering and peeling and require emergency treatment. A genetic marker called HLA-B*1502, more common in people of Southeast Asian descent, is associated with a higher risk. Genetic testing before starting the medication can identify people who carry this marker.
There’s also an important cross-reactivity with carbamazepine, a closely related medication. About 25 to 30% of people who’ve had an allergic reaction to carbamazepine will also react to oxcarbazepine. If you’ve ever had a bad reaction to carbamazepine, make sure your prescriber knows.
A separate allergic condition called DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms) can also occur. This involves fever, rash, and inflammation of internal organs. Some cases have been fatal. Anaphylaxis and angioedema, including swelling of the throat and lips, have been reported rarely.
Mood Changes and Suicidal Thinking
Like all seizure medications, oxcarbazepine carries an FDA warning about an increased risk of suicidal thoughts or behavior. This applies regardless of whether the drug is being used for epilepsy, nerve pain, or mood disorders. The risk is real but statistically small. Pay attention to new or worsening depression, anxiety, agitation, or any thoughts of self-harm, particularly in the first few months or after dose changes.
Stopping the Medication
Oxcarbazepine should not be stopped abruptly. Sudden withdrawal can trigger increased seizure frequency or even status epilepticus, a prolonged seizure that doesn’t stop on its own. If you need to come off the medication, your doctor will taper the dose gradually over a period of weeks. This applies even if you feel the drug isn’t working or the side effects are bothering you.
Pregnancy Considerations
During pregnancy, the body processes oxcarbazepine differently. Blood levels of the drug’s active form gradually decrease as the pregnancy progresses, which can reduce seizure control. This doesn’t mean you should adjust your own dose. Your doctor may monitor drug levels more frequently during pregnancy and adjust accordingly. The decision to continue or change seizure medications during pregnancy involves weighing the risks of uncontrolled seizures against potential effects on the developing baby.