Topamax for weight loss: uses, dosage, side effects

It may sound strange, but one of the drugs most commonly prescribed for weight loss is not FDA-approved for that purpose. It’s a seizure medication called Topamax (topiramate), that happens to come with a welcome side effect for many people: weight loss. Studies have shown that Topamax can help you lose weight by reducing appetite, so many healthcare providers prescribe it off-label for that purpose. It’s not a magic pill, though. This drug can have several side effects, some of them serious. Find out more below.

Studies have found that about 6–17% of people who take Topamax will lose body weight (National Library, 2021). One review of studies found that people with obesity who took Topamax for at least four months lost an average of about 12 pounds more than the placebo group (Kramer, 2011).

Topamax (topiramate) is FDA-approved to treat seizure disorders (like epilepsy) and migraines. Because one of the side effects is decreasing appetite, some providers prescribe Topamax off-label as a weight loss medication. Other common brand names for this drug are: Qudexy XR, Topiragen, and Trokendi XR. 

Topamax is approved by the FDA for the treatment of (National Library, 2021; FDA, 2012): 

• Epilepsy, a neurological disorder in which brain activity becomes abnormal, causing seizures or other types of unusual behavior

• Migraine headaches, which are recurrent, throbbing headaches that typically affect one side of the head

Topamax can also be used “off-label” to treat other conditions, meaning it wasn’t specifically approved by the FDA for those uses. Drugs can be prescribed by a healthcare provider for an unapproved use if they decide that it’s the right treatment for their patient. 

Off-label uses for Topamax include:

• Weight loss

• Alcohol dependence (MedlinePlus, 2021)

Common side effects of Topamax include (Fariba, 2021; National Library, 2021):

• Paresthesia (tingling or prickling sensations)

• Altered sense of taste

Topamax can have serious side effects:

• Myopia (nearsightedness) and glaucoma

• Vision defects

• Metabolic acidosis

• High blood ammonia levels

• Trouble with thinking or concentration

• Nausea

• Confusion

• Memory problems

• Trouble speaking

• Depression or mood problems

• Suicidal tendencies

• Tiredness or sleepiness

• Serious skin reactions, including rash or blisters

• Kidney stones

• Low body temperature

• Hair loss

Topamax comes in the following forms (National Library, 2021; Medline Plus, 2021):

• Tablets: 25 mg, 50 mg, 100 mg, and 200 mg

• Sprinkle capsules: 15 mg and 25 mg

Because Topamax hasn’t been approved by the FDA for weight loss, no specific dosage is recommended for that use. Your healthcare provider will recommend a dose based on your health history, physical condition, and other factors.

• Pregnant women shouldn’t take Topamax because it can increase the risk of congenital anomalies (especially cleft lip and cleft palate) in the infant.

• Acute myopia and glaucoma—rare but possible side effects of Topamax—can lead to permanent vision loss.  

• Metabolic acidosis, in which too much acid is produced in the body, can lead to shock or death when severe.

• Antiepileptic drugs, including Topamax, can increase suicidal thoughts or behavior.

Topamax can interact with the following drugs (National Library, 2021):

• Antiepileptic drugs—Taking phenytoin and carbamazepine with Topamax can decrease blood levels of Topamax. Taking valproic acid with Topamax may cause low body temperature and high levels of ammonia.

• Carbonic anhydrase inhibitors—Topamax is a carbonic anhydrase inhibitor. Taking it with other such medications (like zonisamide and acetazolamide) can increase the risk of metabolic acidosis and kidney stones.

• Central nervous system (CNS) depressants—Topamax alone may cause CNS depression, so it should be used with extreme caution with other CNS depressants, like alcohol.

• Combination oral contraceptives (birth control pills)—Topamax may cause combination oral contraceptives to be less effective.

• Hydrochlorothiazide (HCTZ)—HCTZ is a diuretic (water pill). Taking it together with Topamax can cause concentrations of Topamax to rise, which could be dangerous.

• Lithium—Lithium is used to treat bipolar disorder and other mental illnesses. Taking it together with Topamax can increase the blood levels and effects of lithium.

• Amitriptyline—Amitriptyline is used to combat depression. Taking it together with Topamax can cause a large increase in the concentration of amitriptyline.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

November 17, 2021

Written by

Alison Dalton

Fact checked by

Steve Silvestro, MD

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About the medical reviewer

Steve Silvestro, MD, Ro

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.