Everything you should know about Qsymia for weight loss

GLP-1 weight-loss medications like Wegovy and Zepbound make headlines for their stats, but for the last decade, the weight-loss medication phentermine/topiramate (Qsymia) has been working quietly in the background. Here’s why it’s worth some recognition.
Published June 20, 2023
Qsymia for Weight LossQsymia for Weight Loss

Sometimes opposites make for the perfect pairings. See: yin and yang. Sweet and salty. (Or the inimitable MC Skat Cat and Paula Abdul in her music video for “Opposites Attract.”) Such is the case for two pharmaceutical powerhouses that couldn’t be more different: phentermine and topiramate. One fires up your nervous system while the other chills it out. But together, under the brand name Qsymia, they deliver significant weight loss. Here’s what you should know.

How does phentermine/
topiramate work for weight loss?

Known under brand names Lomaira and Adipex-P, phentermine was the very first weight-loss oral medication approved by the FDA all the way back in 1959. “[It’s] a stimulant that acts on the central nervous system,” explains Dr. Absalon D. Gutierrez, M.D., an endocrinologist and associate professor of endocrinology at McGovern Medical School at UTHealth in Houston, Texas. By raising levels of the action-oriented hormone noradrenaline, it sends signals to the brain to suppress appetite, he adds.

“Phentermine is also thought to block one of the gut hormones called neuropeptide Y that is known to stimulate appetite,” notes Dr. Jessica Folek, M.D., director of bariatric surgery for Northwell Health’s Long Island Jewish Forest Hills Hospital in New York City.

Topiramate, known under the brand name Topamax, is an anti-seizure drug that was initially introduced as an epilepsy treatment in 1996. According to Folek, obesity experts aren’t really sure how topiramate curbs hunger, but they think it works on brain chemicals to restrict the release of glutamate, another neurotransmitter that plays a role in appetite. With less glutamate in the brain, you feel fuller faster, Folek explains.

Taken together, the combination of phentermine and topiramate make for an effective medication for treating obesity.

Is phentermine/
topiramate FDA-approved for weight loss?

Yes. The combination of phentermine and topiramate, under the brand name Qsymia, got the green light for chronic weight management in 2012. It’s FDA-approved for people with a BMI of 30 (or 27 if they also have a weight-related health condition like diabetes or high cholesterol). A healthcare provider may increase the dose depending on someone’s response to the medication.

How much weight can you lose on Qsymia (phentermine/

A person can lose around 10% to 11% of their total body weight after a year of taking the max dose (15mg phentermine/92mg topiramate) of Qsymia every day, according to a study published in the Annals of Pharmacotherapy. If they take the standard dose (7.5mg/46mg), they can expect to lose about 8% after a year.

But even people who stayed with the starter dose (3.75mg/23mg) lost 5% of their total body weight in one year. That's enough to reap ample health benefits, like losing inches around your middle, which means less harmful visceral fat known as belly fat. (The more belly fat you have, the higher your risk of developing heart disease and type 2 diabetes, among other conditions.) Other perks include lower blood pressure, blood sugar, and cholesterol levels. These kinds of benefits support the concept of weight health, which isn't about fitting into a certain size of jeans and is about finding the right weight to improve your health and overall well-being.

What are the side effects of phentermine/

Like with all medications, side effects can occur—some stem from the combo, some from the individual drugs.

Common side effects include (listed alphabetically):

  • Constipation
  • Dizziness
  • Dry mouth
  • Headaches
  • Insomnia (mostly due to the phentermine)
  • Loss of taste
  • Numbness or tingling in your arms and legs

Some of the more serious side effects include (listed alphabetically):

  • Birth defects (cleft lip/cleft palate) if taken while pregnant
  • Blurry vision or not seeing as well (a side effect from topiramate)
  • Mood changes, panic attacks, depression, suicidal thoughts
  • Racing heart or slightly rapid heartbeat (a side effect from phentermine)

You should mention the more serious side effects to your provider as soon as possible (for a full list of side effects, please visit the manufacturer’s website). As for headaches, dry mouth, and other common side effects, they may go away as your body adjusts to the medication, says Folek. If you really can’t bear the dry mouth, insomnia, or headaches, then you may have to stop taking Qsymia and try another medication, but you need to consult with your healthcare provider before stopping the medication.

How long can you take phentermine/

Weight-management drugs are generally designed to be taken long-term, like other chronic disease medications, such as those for diabetes and hypertension.

Qsymia is started at the lowest dose for at least two weeks (3.75mg phentermine/23mg topiramate ER). This dose allows the prescribing healthcare provider to check for any side effects before increasing the dose to the next level (7.5mg/37.5mg). The medical weight loss healthcare provider will monitor how someone responds to the medication to decide if they will need an increase in dosage or are getting adequate decrease in hunger and improvement in fullness on the dose they’re taking.

Qsymia is effective in helping with weight loss for most people with obesity, but like any medication, it is not a guarantee. If you haven’t lost much, or any, weight at the end of six months, your provider may take you off Qsymia or recommend another medication. Of course, as with all weight-loss drugs, a patient should also be doing other things to reach their weight-loss goals, says Folek.

“Exercising, eating healthy—all of these things are paramount,” she says. “When we treat patients for obesity, we do a deep dive into their lifestyles, their diet, and other habits. And we focus on that first, along with behavioral counseling. The medication is an adjunct because it's just a tool. But it’s a very effective tool.”

That is WeightWatchers® approach with its WW Clinic offering, which pairs the WeightWatchers program–including its focus on food, activity, stress, sleep, and other healthy habits–alongside weight-loss medications.

What happens if you stop taking Qsymia (phentermine/

First off, a person shouldn’t stop taking the drug cold turkey. Because it contains topiramate, an anti-seizure drug, there’s a chance it can have a rebound effect and set off a seizure if someone taking one of the two top doses stops it suddenly, Folek says. Always taper off under the supervision of a healthcare provider. Just like with other prescription weight-loss medications, someone may also regain any weight lost if they stop the medication.

What these drugs can do is support a healthy eating and exercise plan by impacting the underlying physiology of obesity, she adds. The payoff is better health—and a way to sustain the weight loss.

Tell me more about…how phentermine/
topiramate feels

Phentermine is a stimulant, says Folek. “You could say it is a ‘cousin’ of amphetamine for comparison,” she adds. In fact, the FDA classifies it as a class IV drug, which means there’s a small risk that people can get addicted to it. That said, a study published in the International Journal of Obesity found that the risk is very small.

What does this mean? You might feel a little jittery—at least at first. As your body adjusts, that nervous energy may go away. Or you might find the jittery feelings combined with other symptoms aren’t tolerable, meaning you may need to talk to your healthcare provider about stopping taking Qsymia. (We say this all the time, but: Everybody is different!)

That said, the dose of phentermine in this combo isn’t as high as it would be if you were treated with phentermine alone, notes Gutierrez. So there’s less chance of feeling overly restless.

Topiramate can drum up its own anxious feelings, since it too acts on the brain and nervous system. You might have a bit of brain fog or have tingling in your fingers or toes. Topiramate is often given off-label for migraine headaches and sometimes as a mood stabilizer to people with bipolar disorder, so Qsymia may cause mood changes in certain people, notes Folek.

How does phentermine/
topiramate compare to GLP-1 medications?

Both medications help people lose weight, but the loss is slightly more with GLP-1 drugs. People lost an average of 11% of their body weight after a year on Qsymia, while people on the GLP-1 medication Wegovy, for example, lost around 15% of their body weight in the same time frame, according to the FDA.

Qsymia tends to be more affordable than GLP-1s, though. “Not all insurances cover [GLP-1 drugs]. For some, they’re prohibitively expensive,” notes Folek. While Wegovy is just under $1400 per month without insurance, with Qsymia, you’re more likely to pay around $100-$200 per month without insurance (and about $80 with insurance).

In addition to cost, a healthcare provider should consider a patient’s medical history, weight-loss and health-related goals, and personal preferences to determine the best prescription for them. If you’re squeamish around needles, for example, phentermine/topiramate may be a better option. Qsymia comes in capsules that are taken once a day, while GLP-1 medications are mostly self-administered, weekly injectables. Your provider may also recommend phentermine/topiramate if you have a history of GI problems, since GLP-1 medications can be accompanied with some nausea, vomiting, diarrhea, bloating, or constipation at first.

Is there anyone who shouldn’t take phentermine/

If you’re pregnant, planning to become pregnant, or have unprotected sex, don’t take Qsymia; topiramate has been linked with an increased risk of cleft palate in babies. You also may need to avoid this prescription weight-loss medication if you have any of the following:

Any type of heart issue, like an arrhythmia, prior heart attack, heart failure, or heart valve problem. Phentermine can speed up your heart rate, which may lead to sudden cardiac arrest.

Glaucoma, a condition that causes pressure in the eye. Topiramate can increase the risk of glaucoma, says Folek.

High blood pressure that’s not controlled by medication or being monitored by your provider. There’s a chance that Qsymia might make it worse, Gutierrez says.

A history of depression or suicidal thoughts. Topiramate can have adverse effects on mood in some people.

MAOI use. Phentermine can raise your serotonin levels slightly, so combining it with this antidepressant increases the risk of serotonin syndrome, which can leave you feeling confused or agitated.

The bottom line

While phentermine/topiramate might not be on your radar, it’s a good option for reaching a healthy weight. “Most patients now are turning towards more well-known medications, so I think this drug is kind of falling in popularity,” says Gutierrez. “But this would be the next best thing just in terms of weight loss.” It would probably be covered by your insurance, and it’s generally more affordable. While Qsymia supports weight loss, the results are optimized when accompanied by a lifestyle modification program (like WeightWatchers) for healthy eating, physical activity, sleep, and positive shifts in mindset.

This content is for informational purposes only and does not constitute medical advice, diagnosis or treatment. It should not be regarded as a substitute for guidance from your healthcare provider.