Anticonvulsant Side Effects: Common, Serious & Long-Term
Anticonvulsants as a class are highly effective for seizures, nerve pain, and mood disorders, but they carry significant neurological side effects — most notably sedation, cognitive slowing, and mood changes that vary considerably by drug. All antiepileptic drugs carry a black box warning for increased risk of suicidal thoughts, and some (particularly lamotrigine) carry risk of life-threatening skin reactions if not started correctly.
Overview
Anticonvulsants — also called antiepileptic drugs (AEDs) — are a pharmacologically diverse group used to treat epilepsy, nerve pain, bipolar disorder, and migraine prevention. Common members include gabapentin (Neurontin), pregabalin (Lyrica), topiramate (Topamax), lamotrigine (Lamictal), and levetiracetam (Keppra). Despite belonging to the same functional category, these drugs work through different mechanisms and have meaningfully different side effect profiles.
Understanding which side effects belong to which drug helps patients and caregivers communicate concerns effectively and work with their prescriber to find the best-tolerated option for their specific condition.
Common Side Effects
Sedation and Dizziness — Gabapentin & Pregabalin
Gabapentin and pregabalin both bind to the alpha-2-delta subunit of voltage-gated calcium channels, reducing neurotransmitter release throughout the nervous system. The sedating effects are a direct consequence of this broad CNS dampening. Dizziness, drowsiness, and coordination problems (ataxia) are among the most commonly reported side effects, particularly when starting or increasing the dose. These effects often improve with time but may not fully resolve.
Cognitive Slowing — Topiramate ("Dopamax")
Topiramate has gained a well-known nickname among patients and clinicians: "Dopamax." Word-finding difficulty, memory problems, slowed thinking, and difficulty concentrating are so common that they represent a significant reason for discontinuation. The mechanism involves multiple pathways, including carbonic anhydrase inhibition and GABA potentiation. Lower doses and slow titration reduce but do not eliminate cognitive effects.
Mood Changes and Irritability — Levetiracetam ("Kepprage")
Levetiracetam is associated with a distinctive pattern of irritability, agitation, and anger that patients have named "Kepprage." It affects synaptic vesicle protein SV2A in ways that differ from other AEDs, and the resulting behavioral changes can be distressing for both patients and families. Anxiety and depression can also occur. These effects may respond to vitamin B6 supplementation or dose adjustment.
Rash — Lamotrigine
Rash affects a meaningful minority of patients starting lamotrigine. Most rashes are benign, but because some progress to Stevens-Johnson syndrome (see below), all rashes occurring within the first several months of lamotrigine treatment must be evaluated promptly. The risk of serious rash is substantially increased when lamotrigine is added to valproate or when the starting schedule is accelerated.
Serious Side Effects
⚠ Serious warnings — contact your prescriber or seek emergency care if any of the following occur.
Stevens-Johnson Syndrome (SJS) — Lamotrigine
Stevens-Johnson syndrome is a rare but potentially fatal reaction in which the skin and mucous membranes blister and slough off, resembling a severe burn. Lamotrigine carries the highest risk of SJS among commonly used AEDs, and the risk is markedly increased by rapid dose escalation or concurrent use of valproate. Early warning signs include a spreading rash, blistering, mouth sores, and eye redness. Any rash on lamotrigine should be evaluated immediately — do not assume it is benign.
Suicidality — All Anticonvulsants (Black Box Warning)
The FDA mandates a black box warning on all antiepileptic drugs for increased risk of suicidal thinking and behavior. Patients initiating any AED should be monitored closely for mood changes, unusual behavior, or thoughts of self-harm, particularly during the first weeks of therapy. This warning applies regardless of the indication (seizures, pain, mood disorder, or migraine).
Respiratory Depression with Opioids — Gabapentin & Pregabalin
Gabapentin and pregabalin significantly increase the risk of respiratory depression when combined with opioids, benzodiazepines, or other CNS depressants. This combination has contributed to a substantial number of overdose deaths. The FDA added a black box warning about this risk in 2019. Patients on both gabapentinoids and opioids require careful monitoring, especially elderly patients and those with underlying respiratory conditions.
Kidney Stones — Topiramate
Topiramate inhibits carbonic anhydrase, which reduces urinary citrate (a natural stone inhibitor) and increases urinary pH, creating conditions favorable for calcium phosphate stone formation. The risk is dose-related. Patients on topiramate are advised to maintain adequate hydration. Any flank pain, blood in urine, or difficulty urinating should be evaluated.
Long-Term Effects
- Weight gain (gabapentin, pregabalin): Increased appetite and fluid retention are common with long-term gabapentinoid use. Weight changes of 5–10% or more are reported in a significant portion of long-term users.
- Weight loss (topiramate): Topiramate reliably reduces appetite and body weight, which is why it is also used off-label and in combination products for obesity treatment.
- Bone density loss: Multiple anticonvulsants — particularly enzyme-inducing AEDs such as phenytoin and carbamazepine, but also valproate — are associated with reduced bone mineral density over time, increasing fracture risk. Patients on long-term AED therapy may benefit from vitamin D and calcium monitoring.
- Hormonal effects (topiramate): Topiramate can reduce the effectiveness of hormonal contraceptives, particularly at higher doses.
- Dependence risk (gabapentin, pregabalin): Both drugs carry abuse potential, and abrupt discontinuation after prolonged use can cause withdrawal symptoms including anxiety, insomnia, and, in some cases, seizures. Tapering is recommended when stopping.
Who Is Most at Risk
- Elderly patients — more sensitive to sedation, falls, and cognitive effects from gabapentin and pregabalin
- Patients with renal impairment — gabapentin and pregabalin are renally cleared; dose adjustment is required to avoid toxicity
- Those on concurrent opioids or benzodiazepines — markedly increased risk of respiratory depression with gabapentinoids
- Patients with a history of depression or suicidality — require close monitoring when starting any AED
- Children and adolescents — behavioral side effects of levetiracetam may be more pronounced in pediatric patients
- Pregnant women — most AEDs carry risks to fetal development; valproate in particular is associated with neural tube defects and developmental delay
Managing Side Effects
Many anticonvulsant side effects are dose-related and improve with slower titration, dose reduction, or switching to an alternative agent. Never stop an anticonvulsant abruptly — doing so can trigger rebound seizures even in people who have been seizure-free for years. Always work with your prescriber before making any changes.
- Report any rash to your prescriber immediately if you are taking lamotrigine
- Tell your prescriber about all other medications, especially opioids, before starting gabapentin or pregabalin
- For cognitive effects on topiramate, ask about the lowest effective dose or alternative agents
- For mood or behavioral changes on levetiracetam, ask about vitamin B6 supplementation or adjunctive therapy
- Maintain adequate hydration on topiramate to reduce kidney stone risk
- Report any new depression, anxiety, or unusual mood changes regardless of which AED you are taking
Frequently Asked Questions
What is 'Kepprage' and why does levetiracetam cause mood changes?
"Kepprage" is a patient-coined term for the irritability, mood swings, and anger that some people experience on levetiracetam (Keppra). The exact mechanism is not fully understood, but levetiracetam modulates synaptic vesicle protein SV2A in ways that differ from other anticonvulsants. Adding vitamin B6 (pyridoxine) sometimes helps; prescribers may also consider dose adjustment or switching medications if mood changes are severe.
Why is lamotrigine titrated slowly, and what is Stevens-Johnson syndrome?
Lamotrigine must be started at a low dose and increased gradually over weeks because rapid titration dramatically increases the risk of Stevens-Johnson syndrome (SJS), a rare but life-threatening skin reaction where large areas of skin blister and slough off. If any rash develops while starting lamotrigine, it should be treated as potentially serious until a clinician evaluates it. The risk is higher when lamotrigine is combined with valproate.
Does gabapentin cause weight gain?
Yes. Weight gain is a well-documented side effect of both gabapentin (Neurontin) and pregabalin (Lyrica). It appears to result from increased appetite and fluid retention. The effect is dose-related and more pronounced with longer-term use. Topiramate, by contrast, tends to cause weight loss.
What is the black box warning that applies to all anticonvulsants?
The FDA requires a black box warning on all antiepileptic drugs (AEDs) stating that they increase the risk of suicidal thoughts and behavior. This risk is small in absolute terms but applies across the entire drug class. Patients starting any AED should be monitored for new or worsening depression, unusual mood or behavioral changes, and any thoughts of self-harm.
Related Drugs
⚠ This article is for informational purposes only and does not constitute medical advice. Never stop or change an anticonvulsant without guidance from your prescriber — abrupt discontinuation can cause seizures.