Qsymia vs. phentermine: Differences, similarities & side effects

In this article:

• Key differences
• Conditions treated
• Is Qsymia better than phentermine?
• Insurance coverage and cost comparison
• Side effects
• Drug interactions
• Drug warnings

In this article

• Key differences
• Conditions treated
• Is Qsymia better than phentermine?
• Insurance coverage and cost comparison
• Side effects
• Drug interactions
• Drug warnings

Qsymia and phentermine are medications commonly prescribed for weight loss. Qsymia is a brand-name drug that contains two active ingredients, phentermine and extended-release topiramate. Phentermine is a generic drug, commonly known by brand names Adipex-P and Lomaira. While both drugs are commonly used for weight management, they are not exactly the same. Continue reading to learn more about Qsymia and phentermine.  

Qsymia vs. phentermine: Key differences

Qsymia contains two active ingredients: phentermine and extended-release topiramate. It is a brand-name drug in the form of oral capsules taken once daily. There is no generic for Qsymia at this time. Phentermine, which is one of the two active ingredients in Qsymia, also exists as its own medication in generic form as well as brand-names Adipex-P and Lomaira. Phentermine is available as oral capsules and tablets. 

Compare Qsymia vs. phentermine key differences
	Qsymia	Phentermine
Drug class	Sympathomimetic amine anorectic (appetite suppressant)/anticonvulsant	Sympathomimetic amine anorectic (appetite suppressant)
Brand/generic status	Brand	Generic; also available as brand-name
Generic or brand name	No generic available at this time	Brand names Adipex-P and Lomaira
What form(s) does the drug come in?	Oral capsules	Oral capsules Oral tablets
What is the standard dosage?	Starting dose is 3.75 mg/23 mg (phentermine/topiramate) by mouth once daily for 14 days, then the prescribing healthcare provider will gradually increase the dose to a maximum dose of 15 mg/92 mg by mouth once daily	The dose of phentermine is 15 to 37.5 mg by mouth once daily; or 8 mg by mouth 3 times daily
How long is the typical treatment?	Long-term	Short-term, although some healthcare providers prescribe it longer-term with close monitoring
Who typically uses the medication?	Adults and pediatric patients 12 years and older	Adults 17 years and older

 

Qsymia vs. phentermine: Conditions treated

Qsymia is approved by the Food and Drug Administration (FDA) for weight loss and long-term weight management in adults and pediatric patients 12 years and older with obesity. It is also FDA approved for use in adults who are overweight and have at least one weight-related medical condition, such as Type 2 diabetes, high blood pressure, or high cholesterol. 

While Qsymia is FDA approved for long-term use, phentermine as a single-ingredient drug is FDA-approved for short-term use in weight loss. It is approved in adults 17 years and older with obesity (with a starting body mass index, or BMI, of 30 or more) or who are overweight (starting BMI of 27 or more) with other weight-related conditions. Although phentermine is FDA approved for short-term use only, healthcare providers sometimes prescribe it off-label (for non-FDA-approved use) for long-term weight management. 

Healthcare providers typically recommend lifestyle changes, including a reduced-calorie diet and increased physical activity, in combination with Qsymia or phentermine. 

Compare Qsymia vs. phentermine conditions treated
Condition	Qsymia	Phentermine
Weight loss and long-term weight management	Yes	Off-label
Weight loss (short-term use)	No	Yes

 

Is Qsymia better than phentermine?

There are no studies that directly compare Qsymia with phentermine alone. Phentermine alone works by reducing appetite, which decreases food consumption—and other metabolic effects may play a role. Qsymia contains phentermine, so it works the same way, but it also contains the active ingredient topiramate, which is thought to work by suppressing appetite and increasing feelings of fullness. 

In a study on Qsymia, people lost up to 10% of their starting body weight after 13 months. Up to 70% of people lost at least 5% of their starting body weight, and about half lost at least 10% of their starting body weight. 

In a review of clinical trials lasting from two to 24 weeks, people taking phentermine lost about 14 pounds.

Currently, weight loss drugs like Wegovy (semaglutide) and Zepbound (tirzepatide) are very popular. While both drugs are effective, a study published in December 2024 found that, on average, people who used Zepbound lost an average of 20.2% of body weight compared to 13.7% in those who used Wegovy.

Consult your healthcare provider for more information and medical advice about the best medication for you—as the best medicine depends on individual factors like your medical history, current conditions, and other medicines you take that could interact with Qsymia or phentermine. 

Qsymia vs. phentermine: Insurance coverage and cost comparison

Qsymia may be covered by insurance plans, depending on the plan. You can check the manufacturer’s website for more information on insurance coverage as well as other savings options. Phentermine may or may not be covered, depending on the plan. Medicare prescription plans do not typically cover weight loss drugs like Qsymia or phentermine.  

For individuals paying out-of-pocket, a 30-day supply of Qsymia costs about $274. You can use a free SingleCare coupon to pay as low as $173, saving about $100 per month on this drug.

Without insurance, generic phentermine costs about $51 for a one-month supply. However, you can use a free SingleCare coupon to pay as low as $10 for this drug, saving about $41 per month.

Compare Qsymia vs. phentermine cost and coverage
	Qsymia	Phentermine
Typically covered by insurance?	Varies	Varies
Typically covered by Medicare Part D?	No	No
Quantity	30, 7.5/46 mg capsules	30, 37.5 mg tablets
SingleCare cost*	$173	$10

*Cost at time of publication. Drug prices fluctuate and vary by pharmacy and location. 

Qsymia vs. phentermine: Side effects

The most common side effects of Qsymia include numbness and tingling, dizziness, altered taste, insomnia, constipation, and dry mouth. 

Phentermine is chemically similar to amphetamine and thus has some similar side effects to stimulant drugs like Adderall. Some of the common side effects of phentermine include palpitations, increased blood pressure, fast heart rate, overstimulation, restlessness, insomnia, mood changes, shaking, headache, dry mouth, altered taste, changes in libido, and stomach issues like diarrhea or constipation. (Although Qsymia also contains phentermine, the dose of phentermine in Qsymia is lower than the typical dose used in phentermine alone. As a result, the risk of stimulant-like side effects may be reduced when using Qsymia compared to taking phentermine by itself.)

The table below lists some of the more common side effects of Qsymia and phentermine. The frequency varies by dosage, with higher doses generally causing a higher frequency of side effects. This is not a full list of potential side effects. For more information on side effects or to discuss any concerns, consult your healthcare provider. 

Compare Qsymia vs. phentermine side effects
	Qsymia		Phentermine
Side effect	Applicable?	Frequency	Applicable?	Frequency
Numbness and tingling	Yes	4–20%	No	N/A
Dizziness	Yes	3–9%	Yes	Not supplied
Altered taste	Yes	1–9%	Yes	Not supplied
Insomnia	Yes	5–9%	Yes	Not supplied
Constipation	Yes	8–16%	Yes	Not supplied
Dry mouth	Yes	7–19%	Yes	Not supplied

Source: Qsymia (DailyMed), Adipex-P (DailyMed)

Qsymia vs. phentermine: Drug interactions

Before taking Qsymia or phentermine, tell your healthcare provider about all of the medicines you take. This includes prescription and over-the-counter (OTC) drugs, vitamins, and dietary supplements. 

Phentermine (and Qsymia, which contains phentermine) should never be taken within 14 days of taking a drug in the monoamine oxidase inhibitor (MAOI) class of drugs because of the risk of hypertensive crisis (a sudden, severe increase in blood pressure). Neither phentermine nor Qsymia should be combined with alcohol. Also, people who use insulin or take oral medication to lower blood sugar may require lower doses of their blood sugar-lowering medicines when taking phentermine or Qsymia. 

Qsymia, due to its topiramate component, has some additional interactions, such as birth control pills. This interaction does not tend to increase the risk of pregnancy but may result in spotting. Other Qsymia interactions include central nervous system (CNS) depressants, amitriptyline, and certain anticonvulsants, among others. 

This is not a full list of drug interactions, and others may occur. Consult your healthcare provider for more information about drug interactions and how they may affect you. 

Compare Qsymia vs. phentermine drug interactions
Drug	Drug class	Interacts with Qsymia?	Interacts with  Phentermine?
Phenelzine  Tranylcypromine	MAOI	Yes	Yes
Alcohol	Alcohol	Yes	Yes
Lantus  Novolog  Tresiba	Insulin	Yes	Yes
Glipizide  Glyburide	Oral diabetes medications	Yes	Yes
Kariva Ocella Sprintec	Oral contraceptives (birth control pills)	Yes	No
Phenobarbital  Benzodiazepines such as Xanax (alprazolam) Sleep medications such as Ambien (zolpidem)	CNS depressants	Yes	No
Carbamazepine  Phenytoin  Valproic acid	Anticonvulsants	Yes	No
Amitriptyline	Tricyclic antidepressant	Yes	No

 

Phentermine vs. Qsymia: Drug warnings

Be sure to tell your healthcare provider about your medical history and all current medical conditions before taking phentermine or Qsymia.

You should not take phentermine or Qsymia if:

• You are pregnant or breastfeeding
• You have glaucoma
• You have an overactive thyroid (hyperthyroidism)
• You have taken an MAOI in the last 14 days
• You are allergic to any ingredient in the medication

Additionally, you should not take phentermine if you have a history of heart disease, other heart problems, or a history of substance abuse. People with these conditions should check with their healthcare provider before taking Qsymia.

Warnings that apply to both phentermine and Qsymia include:

• Avoid alcohol when taking phentermine or Qsymia. 
• Do not drive or operate machinery until you know how phentermine or Qsymia affects you. 
• Phentermine and Qsymia are controlled substances, which means they have a risk of abuse and dependence. Tell your healthcare provider if you have a history of substance use disorder. 
• If you have symptoms of an allergic reaction, such as hives, trouble breathing, or swelling of the face, lips, tongue, or throat, get emergency medical help. 

Additional warnings of Qsymia, due to its topiramate component, include:

• Qsymia can cause harm to an unborn baby. Those who can become pregnant should use effective birth control while taking Qsymia and should be tested for pregnancy before starting Qsymia and monthly during treatment. You can discuss birth control options with your healthcare provider.
• Qsymia may cause suicidal thoughts or behaviors. Call your healthcare provider right away if you have depression, changes in mood or behavior, or thoughts of suicide. You can call or text 988 for the Suicide & Crisis Lifeline if you need help right away. 
• Qsymia can cause eye problems. If you have any changes in vision, stop taking Qsymia and call your healthcare provider right away. 
• Serious, life-threatening skin reactions may occur. Stop taking Qsymia and get emergency medical help if you have a skin rash, fever, sore throat, burning eyes, skin pain, or blistering or peeling skin. 

With phentermine alone, there have been rare cases of cardiac valvular disease and pulmonary hypertension (high blood pressure of the lungs). Talk with your healthcare provider about these risks. 

Bottom line 

Qsymia contains phentermine and extended-release topiramate and is used for long-term weight management. Phentermine alone is also used for weight loss—it is FDA approved for short-term use but sometimes prescribed off-label for a longer period of time. There are various risks and benefits with both of these medications, and there are also other options for weight loss. Consult your healthcare provider if you are considering either drug, switching from one to another, or would like to explore other treatment options.