Updated on March 5, 2026 by Amy Harris, MS, RN, CNM. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.
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Table of contents
- What Is Phentermine?
- What Is Ozempic®?
- How Do Weight Management Medications Work?
- Who Can Take Phentermine, Qsymia®, and Ozempic®?
- What Are the Differences between Ozempic®, Phentermine, and Qsymia®?
- What Are the Side Effects of Ozempic®, Phentermine, and Qsymia®?
- How Do I Choose: Ozempic® vs. Phentermine?
- Related Content
It seems like every day there is news about a new breakthrough weight-loss medication. Doctors and researchers continue working to develop treatments that are both effective and safe for long-term weight management. Two medications that often come up in discussions about prescription weight loss treatments are phentermine and Ozempic®. Understanding how these medications work, their potential side effects, and whether they may be appropriate for you can be an important step in your weight management journey.
What Is Phentermine?
Phentermine (pronounced fen' ter meen) is a medication used to support weight loss. The brand names for phentermine in the United States include Adipex-P® and Lomaira®. It is one of the oldest FDA-approved weight loss medications and has been available since 1959.[1]
A newer weight-loss medication called Qsymia® (pronounced kew-sim-EE-a) combines phentermine with topiramate in an extended-release capsule.[2] Qsymia® may also be prescribed to help some individuals maintain weight loss over a longer period of time.[3]
What Is Ozempic®?
Ozempic® is the brand name of a medication called semaglutide. Semaglutide belongs to a class of medications known as glucagon-like peptide-1 receptor agonists (GLP-1 agonists). These medications mimic natural hormones in the body that help regulate blood sugar levels and appetite, which can support weight loss in some individuals.[4,5]
How Do Weight Management Medications Work?
Phentermine and Ozempic® work differently to help people lose weight. Phentermine supports weight loss primarily by suppressing appetite, helping individuals consume fewer calories.[1]
Both phentermine and Ozempic® can help people feel fuller for longer between meals.[1,5] While Ozempic® is FDA-approved to treat type 2 diabetes, healthcare providers sometimes prescribe it “off-label” to help support weight management. Off-label means that an approved drug is being used for a purpose other than its original FDA-approved indication.[6]
Ozempic® may contribute to weight loss by slowing digestion, stabilizing blood sugar levels, and reducing appetite and food cravings.[7,8]
Regardless of the medication prescribed, weight management treatments tend to work best when combined with dietary changes and increased physical activity.[4]
Who Can Take Phentermine, Qsymia®, and Ozempic®?
Healthcare providers prescribe weight loss medications such as Qsymia® and Ozempic® based on BMI and other health conditions a patient may have.
Phentermine is FDA-approved for treating overweight or obesity in individuals with a BMI greater than 30, or a BMI of at least 27 with related conditions such as diabetes or hyperlipidemia. In some cases it may also be prescribed for patients with controlled hypertension and a BMI above 27.[1]
The FDA approved Qsymia® for adults with a BMI of 30 or higher, or a BMI of 27 or greater with at least one weight-related condition. It is also approved for pediatric patients aged 12 years and older whose BMI falls within the 95th percentile for their age and sex.[2]
Ozempic® is FDA-approved for adults with type 2 diabetes to help lower blood sugar levels and reduce the risk of cardiovascular events such as heart attack or stroke in those with existing heart disease.[5]
Pregnant individuals, those planning to become pregnant, or those who are breastfeeding should not take phentermine, Qsymia®, or Ozempic®. Taking Qsymia® during pregnancy may increase the risk of birth defects such as cleft lip or cleft palate.[2]
Healthcare providers are often cautious when prescribing phentermine for adults over the age of 65. If you are over 65, your healthcare provider may recommend other weight management treatments that may be safer.[1]
Phentermine and Qsymia® may not be appropriate for individuals with heart disease, high blood pressure, hyperthyroidism, or glaucoma.[1-3] People with the following conditions should discuss risks and treatment options with a healthcare provider before taking phentermine, Qsymia®, or Ozempic®[1-4]:
- High blood pressure
- Glaucoma
- Thyroid conditions
- Heart disease or atherosclerosis
- Mood disorders such as depression
What Are the Differences between Ozempic®, Phentermine, and Qsymia®?
To help compare these medications, here are several key differences between Ozempic®, phentermine, and Qsymia®.[1,7,8]
| Feature | Ozempic® | Phentermine | Qsymia® |
|---|---|---|---|
| How it’s taken | Self-administered injection | Oral tablet | Extended-release oral capsule |
| Dosing schedule | Injected once weekly | Taken daily | Taken daily |
| Addiction potential | Not considered habit-forming | May be habit-forming | Not considered habit-forming |
| Typical treatment duration | Often used long-term | Usually prescribed short-term (3–6 weeks) | May be used for longer-term weight management |
| Primary use | Treats type 2 diabetes and may support weight loss | Weight management | Weight management |
What Are the Side Effects of Ozempic®, Phentermine, and Qsymia®?
Side effects can play a significant role in deciding which medication may be appropriate. Research suggests that about 30 percent of people stop taking prescription medications due to side effects.[9]
Common side effects of phentermine include[4]:
- Sleeplessness
- Constipation
- Faster heart rate
- Nervousness
Common side effects reported with Qsymia® include[2]:
- Numbness or tingling in the hands, arms, feet, or face
- Dizziness
- Changes in taste
- Insomnia
- Constipation
- Dry mouth
Approximately five out of 100 people taking Ozempic® report common side effects such as:
- Nausea
- Vomiting
- Diarrhea
- Abdominal pain
- Constipation
Less common Ozempic® side effects may include gas, indigestion, stomach upset, jaundice, or fever.[10]
How Do I Choose: Ozempic® vs. Phentermine?
If you’re trying to decide between medications, you may be wondering which option is most effective. A large analysis of existing weight loss medication studies found that Qsymia® and GLP-1 receptor agonists such as semaglutide are among the most effective treatments for reducing body weight in adults with overweight or obesity.[11]
Cost is also an important factor when choosing a weight management medication. Prescription weight loss medications can be expensive, and insurance coverage varies depending on the medication and the reason it is prescribed. Checking with your insurance provider can help clarify what treatments may be covered.
If you're still feeling unsure about your options, speaking with a licensed healthcare provider can help you better understand which treatments may be appropriate for your health history and weight management goals.
Some individuals choose to explore telehealth weight management programs that connect patients with licensed clinicians who can evaluate eligibility for medications like GLP-1 therapies and develop individualized treatment plans.
Related Content
Jardiance® vs. Ozempic®: Similarities and Differences
References
- Phentermine. MedlinePlus. https://medlineplus.gov/druginfo/meds/a682187.html. Accessed October 16, 2023.
- Qysymia Full Prescribing Information. Vivus LLC. https://qsymia.com/. Published 2023. Accessed October 16, 2023.
- Phentermine; Topiramate extended-release capsules. Cleveland Clinic. https://my.clevelandclinic.org/health/drugs/18941-phentermine-topiramate-extended-release-capsules. Accessed October 17, 2023.
- Prescription weight-loss drugs. Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/weight-loss-drugs/art-20044832. Published October 29, 2022. Accessed October 17, 2032.
- FAQs | Ozempic® (semaglutide) injection 0.5 mg, 1 mg, or 2 mg. novoMEDLINK. https://www.novomedlink.com/diabetes/products/treatments/ozempic.html. Accessed October 17, 2023.
- Understanding Unapproved Use of Approved Drugs “Off Label.” FDA. https://www.fda.gov/patients/learn-about-expanded-access-and-other-treatment-options/understanding-unapproved-use-approved-drugs-label. Accessed October 17, 2023.
- Prescription medications to treat overweight and obesity. NIDDK. https://www.niddk.nih.gov/health-information/weight-management/prescription-medications-treat-overweight-obesity#how. Published March 2023. Accessed October 16, 2023.
- Jeong D, Priefer R. Anti-obesity weight loss medications: Short-term and long-term use. Life Sci. 2022;306:120825. doi:10.1016/j.lfs.2022.120825
- Why do people stop taking their meds? Cost is just one reason. NPR. https://www.npr.org/sections/health-shots/2017/09/08/549414152/why-do-people-stop-taking-their-meds-cost-is-just-one-reason. Published September 8, 2017. Accessed October 16, 2023.
- Semaglutide (Subcutaneous Route) Side Effects - Mayo Clinic. https://www.mayoclinic.org/drugs-supplements/semaglutide-subcutaneous-route/side-effects/drg-20406730?p=1. Published October 1, 2023. Accessed October 17, 2023.
- Shi Q, Wang Y, Hao Q, et al. Pharmacotherapy for adults with overweight and obesity: a systematic review and network meta-analysis of randomised controlled trials. Lancet. 2022; 399(10321):259-269.
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