Topiramate — NZ Medication Guide
✅ Reviewed by Ramon Wong, BPharm, Registered Pharmacist (New Zealand) | May 2026
This information is for educational purposes only and is not a substitute for personalised advice from your doctor or pharmacist. Always seek professional guidance before making changes to your medications.
What is Topiramate?
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Topiramate is an anticonvulsant used for epilepsy and migraine prevention. This medication is funded by Pharmac for epilepsy; not funded for migraine prevention.
What is Topiramate Used For?
Used as monotherapy or adjunct for focal seizures and generalised tonic-clonic seizures, and for migraine prophylaxis.
How Does Topiramate Work?
Blocks voltage-gated sodium channels, enhances GABA-A activity, antagonises AMPA/kainate glutamate receptors, and weakly inhibits carbonic anhydrase — reducing neuronal excitability.
How to Take Topiramate
Start at 25–50 mg/night and titrate slowly. Migraine prophylaxis: 50–100 mg/day in two divided doses. Epilepsy: up to 400 mg/day. Drink at least 2L water daily to reduce kidney stone risk.
Common Side Effects of Topiramate
- Cognitive slowing and word-finding difficulty (“brain fog” — dose-dependent)
- Paraesthesia (tingling in hands and feet — very common)
- Fatigue
- Anorexia and weight loss
- Mood changes
Serious Side Effects — Seek Medical Attention
Contact your doctor or call 111 immediately if you experience any of the following:
- Kidney stones (increase fluid intake)
- Acute angle-closure glaucoma (sudden eye pain/vision change — stop and seek urgent care)
- Metabolic acidosis
- Oligohidrosis and hyperthermia (especially in children)
- Teratogenicity (cleft palate, IUGR)
Drug Interactions
Topiramate may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:
- Sodium valproate (increased hyperammonaemia risk)
- Combined oral contraceptive pill (topiramate reduces oestrogen — use additional contraception)
- Carbonic anhydrase inhibitors (increased kidney stone risk)
New Zealand Prescribing Information
Topiramate (25 mg, 50 mg, 100 mg tablets — Topamax® and generics) is funded for epilepsy only. Not funded for migraine prevention — requires private purchase. Women of childbearing age must use effective contraception (note: topiramate reduces COC efficacy).
Frequently Asked Questions
Will topiramate affect my memory?
Cognitive side effects (“brain fog”, word-finding difficulty) are dose-dependent and common. Slow titration minimises this. If severe, discuss a dose reduction with your neurologist.
How do I reduce kidney stone risk on topiramate?
Drink at least 2 litres of water daily, stay hydrated, and avoid dehydration. Topiramate increases urinary calcium phosphate stone formation risk.
⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.
Reviewed by a Registered Pharmacist NZ
References & Further Information
The following New Zealand and international resources were used to inform this page: