Young woman researching Ozempic vs. Phentermine on laptop

Ozempic® vs. Phentermine: What's the Difference?

Written on October 30, 2023 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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It seems like every day, there is news of a new miracle weight-loss drug, doesn’t it? Doctors and scientists are working hard to develop more effective medicines with fewer side effects to advance the science of weight loss management. Two of the seven FDA-approved weight management drugs are phentermine and Ozempic®. Learning about how they work, their side effects, and whether or not they are a safe medication for you can be an essential part of your weight management journey.

What Is Phentermine?

Phentermine (pronounced fen' ter meen) is a type of medication taken to cause weight loss. The brand names for phentermine in the United States are Adipex-P® and Lomaira®. It is one of the oldest FDA-approved weight loss medications – it 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® is also sometimes used by doctors to help people maintain weight loss over the longer term.[3]

What Is Ozempic®?

Ozempic® is the brand name of a medication called semaglutide. Semaglutide belongs to a category of medicines called glucagon-like peptide-1 receptor agonists or GLP-1 agonists. It mimics hormones in your body to help regulate blood sugar and support weight loss.[4,5]

How Do Weight Management Medications Work?

Phentermine and Ozempic® work differently to help people lose weight. Phentermine helps you to lose weight by decreasing your appetite, so you eat less.[1]

Phentermine and Ozempic® can help you feel fuller for longer between meals.[1,5] While Ozempic® is FDA-approved to treat type 2 diabetes, healthcare providers use it “off-label” to help with weight management. Off-label means that an approved drug is being used for an unapproved use (to treat obesity, in this case).[6]

Ozempic® causes weight loss by improving fat metabolism, stabilizing blood sugars, slowing digestion, and curbing food cravings by suppressing appetite.[7,8]

All weight management medications work faster and more effectively when combined with eating a lower-calorie diet and increasing your physical activity.[4]

Who Can Take Phentermine, Qsymia®, and Ozempic®?

Healthcare providers prescribe weight loss drugs such as Qsymia® and Ozempic® based on your BMI and other medical conditions you might have.

The FDA-approved phentermine for treating overweight and obesity if your BMI is higher than 30 or is at least 27 and you have diabetes or hyperlipidemia (high lipids). Phentermine can also be prescribed to hypertension patients above BMI 27, but only if their blood pressure is appropriately controlled.[1]

The FDA approved Qsymia® for adult patients with a body mass index (BMI) of 30+ or 27 kg/m2 or greater (overweight) with at least one weight-related medical condition or pediatric patients aged 12 years and older with an initial BMI in the 95th percentile or greater standardized for age and sex.[2]

Ozempic® is approved by the FDA for adults with type 2 diabetes to lower blood sugar, along with diet and exercise, and reduce the risk of major cardiovascular events such as heart attack, stroke, or death in adults with type 2 diabetes and known heart disease.[5] Therefore, if you have pre-diabetes or type 2 diabetes, Ozempic® may be better than phentermine.

It is unsafe for pregnant (or people planning on becoming pregnant) or breastfeeding people to take phentermine, Qsymia®, or Ozempic®. If you take Qsymia® during pregnancy, your baby has a higher risk for birth defects called cleft lip and cleft palate.[2]

Doctors are cautious in prescribing phentermine for weight loss in people over 65. If you are over age 65, talk with your healthcare provider about some of the other weight loss medications that might be safer.[1]

Phentermine and Qysmia® could harm people with heart disease, high blood pressure, an overactive thyroid gland, or glaucoma.[1-3] If you have any of the following medical diagnoses or conditions, you should talk with your healthcare provider before taking phentermine, Qysmia®, 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 assist you in making sense of the various weight management medications on the market, here is a helpful list of some of the key differences between them [1,7,8]:

  1. Ozempic® is only available as a self-administered injection. Phentermine and Qsymia® are sold as tablets taken by mouth.
  2. You only need to inject Ozempic® once a week, whereas phentermine and Qsymia® are taken daily, 30 minutes before a meal.
  3. Phentermine can be habit-forming, but Ozempic® and Qsymia® are not.
  4. Most people only take phentermine for 3-6 weeks, whereas people taking Ozempic® and Qsymia® usually stay on the medication longer-term, sometimes for years.
  5. Ozempic® is primarily used to treat type 2 diabetes with the side effect of causing weight loss, whereas phentermine and Qsymia® do not treat diabetes.

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What Are the Side Effects of Ozempic®, Phentermine, and Qsymia®?

One out of every three people (30 percent) stop taking prescribed medications because of side effects.[9] So, when deciding which weight loss medication might be right for you, it helps to know what to expect regarding side effects.

The most commonly experienced side effects caused by Phentermine are [4]:

  • Sleeplessness
  • Constipation
  • Faster heart rate
  • Nervousness.

The most common side effects of Qysemia® reported by people taking the medication include [2]:

  • Numbness or tingling in the hands, arms, feet, or face
  • Dizziness
  • Changes in the way foods taste or loss of taste
  • Trouble sleeping (insomnia)
  • Constipation
  • Dry mouth.

Approximately five out of 100 people taking Ozempic® typically report these medication side effects:

  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal pain
  • Constipation

Less common Ozempic® side effects include passing gas, recurrent fever, yellowing of the eyes and skin caused by jaundice, indigestion, and stomach upset.[10]

How Do I Choose: Ozempic® vs. Phentermine?

Now that you know what to expect in terms of possible side effects and which drug is safest for you, you might be wondering, what is the most effective weight loss pill? Some good news is that a recent, large analysis of existing studies of weight loss medications found that in adults with overweight and obesity, Qsymia® and GLP-1 receptor agonists like Ozempic® are the best drugs for reducing weight. The same study reported that of the GLP-1 agonists, semaglutide (Ozempic®) might be the most effective.[11]

Cost is another critical consideration when choosing which weight loss medication is right for you. Weight-loss drugs can be expensive. Be sure to ask your insurance company about your coverage of each of the specific medications you are considering and how long they will pay for them.

Are you still feeling overwhelmed by the options? Everlywell’s online weight loss program, called Weight Care+, connects you with an expert nurse practitioner who can discuss your options. Those people who meet program qualifications may be able to get a weight loss prescription online.

Science and research show us that weight management medications can help people with health problems related to overweight or obesity.[7] Getting the safest and most effective treatment, with the fewest side effects, may help reduce your risk of weight-related chronic diseases such as diabetes, heart disease, arthritis, and some cancers.[7] Everlywell wants you to have a healthier tomorrow with its convenient and accessible telehealth, at-home testing options, and vitamins and supplements.

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  1. Phentermine. MedlinePlus. Accessed October 16, 2023.
  2. Qysymia Full Prescribing Information. Vivus LLC. Published 2023. Accessed October 16, 2023.
  3. Phentermine; Topiramate extended-release capsules. Cleveland Clinic. Accessed October 17, 2023.
  4. Prescription weight-loss drugs. Mayo Clinic. Published October 29, 2022. Accessed October 17, 2032.
  5. FAQs | Ozempic® (semaglutide) injection 0.5 mg, 1 mg, or 2 mg. novoMEDLINK. Accessed October 17, 2023.
  6. Understanding Unapproved Use of Approved Drugs “Off Label.” FDA. Accessed October 17, 2023.
  7. Prescription medications to treat overweight and obesity. NIDDK. Published March 2023. Accessed October 16, 2023.
  8. 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
  9. Why do people stop taking their meds? Cost is just one reason. NPR. Published September 8, 2017. Accessed October 16, 2023.
  10. Semaglutide (Subcutaneous Route) Side Effects - Mayo Clinic. Published October 1, 2023. Accessed October 17, 2023.
  11. 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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