What to Expect When You Start Taking Lacosamide

Starting a new seizure medication comes with questions — and one of the biggest is: what side effects should I expect? If your doctor has prescribed Lacosamide (brand name Vimpat), knowing what's normal and what's not can help you feel more in control of your treatment.

Lacosamide is an antiepileptic drug (AED) that works by selectively enhancing the slow inactivation of voltage-gated sodium channels in the brain. It's FDA-approved for focal seizures and primary generalized tonic-clonic seizures. For a deeper dive into how it works, see our article on Lacosamide's mechanism of action.

Common Side Effects

Most side effects of Lacosamide are mild to moderate and tend to improve as your body adjusts — especially during the initial dose increases. The following side effects are reported most frequently in clinical trials:

• Dizziness — The most common side effect, affecting up to 30-50% of patients at higher doses. Usually worst during dose increases.
• Headache — Reported in about 10-15% of patients.
• Nausea and vomiting — Tends to be most noticeable when you first start or when your dose increases.
• Double vision (diplopia) — Can occur especially at higher doses or when combined with other sodium channel-blocking AEDs.
• Blurred vision — Similar to double vision, usually dose-related.
• Fatigue and drowsiness — May affect your ability to drive or operate machinery, especially in the first few weeks.
• Tremor — Mild shaking of the hands, usually temporary.
• Unsteadiness (ataxia) — Difficulty with coordination or balance.

Good to know: Your doctor will typically start you at a low dose (50 mg twice daily) and increase gradually. This slow titration helps minimize side effects. Most patients find that dizziness and nausea improve significantly within 1-2 weeks at each new dose level.

Serious Side Effects — When to Call Your Doctor

While serious side effects are uncommon, some require immediate medical attention:

Heart Rhythm Changes

Lacosamide can affect your heart's electrical conduction system, specifically the PR interval. This is one of the more unique concerns with this medication. Symptoms to watch for include:

• Feeling like your heart is racing, fluttering, or skipping beats
• Fainting or near-fainting spells
• Feeling lightheaded when standing up
• Shortness of breath

Your doctor may order an EKG before starting Lacosamide and during treatment to monitor your heart rhythm. This is especially important if you have a history of heart problems or take other medications that affect heart rhythm.

Call your doctor immediately or go to the ER if you faint, have an irregular heartbeat, or feel chest pain.

Suicidal Thoughts or Behavior

All antiepileptic drugs carry an FDA warning about an increased risk of suicidal thoughts or behavior. While this risk is small (affecting about 1 in 500 patients across all AEDs), it's important to monitor for:

• New or worsening depression
• Unusual changes in mood or behavior
• Thoughts of self-harm or suicide
• Increased anxiety or agitation

Tell your doctor or a family member right away if you notice these changes. Do not stop Lacosamide suddenly — stopping seizure medication abruptly can cause dangerous rebound seizures.

Severe Allergic Reactions (DRESS Syndrome)

DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms) is a rare but potentially life-threatening allergic reaction. Symptoms typically appear 2-8 weeks after starting a new medication:

• Skin rash (may be widespread)
• Fever
• Swollen lymph nodes
• Facial swelling
• Unusual fatigue or yellowing of the skin/eyes

Seek emergency medical care if you develop a rash with fever, especially in the first few months of treatment.

Syncope (Fainting)

Lacosamide has been associated with fainting episodes, likely related to its effects on heart conduction. If you've fainted or nearly fainted since starting Lacosamide, tell your doctor promptly.

Special Populations

Older Adults

Elderly patients may be more sensitive to Lacosamide's effects on heart rhythm and may experience more dizziness. Dose adjustments may be needed, and cardiac monitoring is especially important.

Kidney or Liver Problems

If you have severe kidney impairment (CrCl ≤30 mL/min) or are on hemodialysis, your doctor may reduce your maximum dose. Lacosamide is not recommended for patients with severe liver disease.

Pregnancy

Lacosamide is classified as Pregnancy Category C, meaning there's potential risk to the fetus. However, uncontrolled seizures during pregnancy can also be dangerous. If you're pregnant or planning to become pregnant, discuss the risks and benefits with your neurologist.

How to Manage Side Effects

Here are practical tips for dealing with common Lacosamide side effects:

• For dizziness: Rise slowly from sitting or lying positions. Avoid driving or operating heavy machinery until you know how the medication affects you.
• For nausea: Take Lacosamide with food. Some patients find taking it with a small meal or snack helps significantly.
• For fatigue: Take your evening dose closer to bedtime. Give your body a few weeks to adjust at each dose level.
• For blurred/double vision: Report this to your doctor — it may indicate the dose is too high or that Lacosamide is interacting with another medication.

Never adjust your dose or stop taking Lacosamide without talking to your doctor first. Abruptly stopping seizure medication can cause rebound seizures, which can be life-threatening.

Final Thoughts

Most people tolerate Lacosamide well, especially when the dose is increased gradually. Common side effects like dizziness and nausea usually improve within a couple of weeks. The more serious concerns — heart rhythm changes, allergic reactions, and mood changes — are uncommon but important to know about.

Stay in close contact with your doctor, especially during the first few months of treatment. And if you're having trouble finding or affording Lacosamide, check out our guides on finding Lacosamide in stock and saving money on your prescription.