Phentermine is a controlled substance, indicating its potential for misuse or dependence. Specific federal and state laws limit the amount of this medication that can be prescribed or dispensed within a certain period of time.
Highlights
- Phentermine, a stimulant, and Wegovy, a GLP-1 receptor agonist, are both weight loss medications.
- Phentermine is intended for short-term use, while Wegovy can be used for longer periods; this may contribute to the greater weight loss seen with Wegovy in some individuals.
- Wegovy has a considerably higher cost than phentermine because phentermine is available as a generic.
- Wegovy is an injectable medication, while phentermine is taken orally.
Phentermine under the brand name Adipex-P was
Wegovy vs. Phentermine: Primary Differences
Wegovy and phentermine are FDA-approved for weight loss in varying populations. Wegovy is approved for adults and children who are 12 and older, while phentermine can be prescribed to those 17 and older.
Age is not the only eligibility requirement. These anti-obesity medications are only approved for those who meet certain body mass index (BMI) criteria:
- A BMI of 30 or greater.
- A BMI of 27 or greater and a weight-related health condition.
While phentermine and Wegovy share these similarities, there are also many differences between the two.
Active Ingredients
Phentermine is the active ingredient of Adipex-P. Wegovy is a brand name for the active ingredient semaglutide. They belong to different drug classes and have differing mechanisms of action.
How They Work
While both Wegovy and phentermine promote weight loss, they do so in different ways.
Wegovy is a glucagon-like peptide-1 (GLP-1) agonist; it mimics the protein GLP-1, which is naturally produced by the body. When receptors link with this protein, you feel fuller. So, by mimicking GLP-1, Wegovy also lessens your appetite, helping you to eat fewer calories and, consequently, lose weight. Wegovy also slows down the speed at which food leaves the stomach, which allows you to feel fuller for longer and have fewer cravings.
Phentermine, on the other hand, is a stimulant and appetite suppressant and belongs to the sympathomimetic anorectic drug class. It works by stimulating the release of neurotransmitters (brain chemicals) dopamine, norepinephrine, and epinephrine. When these neurotransmitters are released, a person has a reduction in appetite, tends to eat less, and this leads to weight loss. Additionally, by activating the nervous system, phentermine may provide a boost of energy that can help with meeting physical activity goals.
For both medications, the best results are seen when combining any of them with a healthy diet and exercise. These lifestyle changes are also crucial for weight maintenance when the medications are eventually discontinued. Such recommendations and ongoing monitoring will be included in your online weight loss plan.
Comparing Efficacy
Both Wegovy and phentermine are effective at treating obesity, but Wegovy may result in more weight loss based on individual studies—the medications have not been directly compared.
Research on phentermine for weight loss has found that it can help 40% of people lose at least 5% of their initial body weight over six months, while clinical trials for Wegovy found that adults experienced an average weight loss of almost 15% over the course of 68 weeks.
Duration of Action
Phentermine is a controlled substance that is only approved for short-term use, up to 12 weeks at a time. This cut-off is in place because your body can develop a tolerance to phentermine after just a few weeks, which can weaken its effects. Additionally, the longer phentermine is used, the greater the risk of misuse and dependency. In some cases, phentermine may be taken for longer than 3 months at a time, but it should only be done with the close supervision of a healthcare professional.
There is also a combination pill of phentermine and topiramate called Qsymia. Unlike phentermine alone, Qsymia is approved for chronic weight management and has demonstrated safety and efficacy in longer-term studies.
In comparison, Wegovy is intended for chronic weight management; it may take months to reach its maintenance dose. However, it is not meant to be a permanent medication, which is why supporting it with a healthy diet and lifestyle changes, such as regular exercise, is crucial to avoid weight gain following the medication’s discontinuation.
Note that booking an appointment doesn’t guarantee obtaining a prescription. The decision is at the discretion of your healthcare provider.
Side Effects
The different mechanisms of action result in differing side effects between the two.
- Stomach pain
- Nausea and vomiting
- Diarrhea
- Constipation
- Burping
- Gas and bloating
Some more serious risks and side effects of Wegovy may also occur, though they are rare:
- Gallbladder problems
- Pancreatitis
- Worsening of diabetes-related eye problems
- Faster heart rate
- Kidney problems
- Hypertension
- Tachycardia
- Vision problems
- Shallow breathing
- Rash or hives
Dosing
Wegovy and phentermine are administered differently, which also affects their dosing.
Wegovy is an injectable medication. The starting dose is typically 0.25 mg once a week. The dose will increase progressively every four weeks until you reach a maintenance dose of either 1.7 or 2.4 mg once weekly, depending on your provider’s instructions.
Phentermine, on the other hand, is available as tablets, orally disintegrating tablets, or capsules. It comes in the following doses:
- Phentermine tablets: 37.5 mg
- Phentermine capsules: 15 mg, 30 mg, and 37.5 mg
Generally, phentermine is taken once a day, either before breakfast or 1 to 2 hours afterward. It is also available in a low-dose 8 mg tablet under the brand name Lomaira, which is taken 3 times a day, 30 minutes before meals.
Interactions
Stimulants, such as phentermine, carry a risk of high blood pressure, and this risk increases if phentermine is taken alongside monoamine oxidase inhibitors (MAOIs), such as the antidepressants Marplan, Nardil, and Emsam. It can also interact with hypoglycemia medicines. Finally, it’s important to avoid alcohol while taking phentermine.
As for Wegovy, its primary drug interactions include medications taken to manage diabetes, such as insulin and oral medications. Since it also prevents blood sugar spikes, taking it alongside other diabetes medications could lead to low blood sugar. Also, since Wegovy slows down gastric emptying, it can affect the absorption of other medications you are taking, so remember to discuss this with your healthcare provider.
Warnings and Precautions
Wegovy carries a boxed warning: thyroid C-cell tumors occurred during animal studies. While
Phentermine does not have any boxed warnings, but there have been some rarely documented life-threatening cases of dangerously high blood pressure and leaking heart valves.
Furthermore, as a stimulant, phentermine should not be taken by those with certain health conditions or factors, such as:
- Overactive thyroid
- History of cardiovascular disease
- Glaucoma
- Agitation
- History of drug abuse
- Pregnancy or breastfeeding
Cost
Wegovy is only available in its brand-name form. Its average monthly cost is $1,430, regardless of dose. Since there is no generic form of semaglutide, the best way to lower the cost of Wegovy is through insurance, although coverage may vary by company.
As for phentermine, the cost averages between $45 to $50 per 30-day supply, based on the dosage. This weight loss medication is priced lower than Wegovy because it is available as a generic.
How do Phentermine and Wegovy Compare?
While both Wegovy and phentermine are approved weight loss medications, they belong to two different drug classes and have differing active ingredients, which causes key differences in their administration route, dosing frequency, cost, and eligibility, as outlined in the table below.
|
Phentermine |
Wegovy |
|
|
Active Ingredient |
Phentermine |
Semaglutide |
|
Drug Class |
Sympathomimetic anorectic (stimulant/appetite suppressant) |
GLP-1 receptor agonist |
|
Form |
Capsule, tablet, or orally disintegrating tablet |
Injectable |
|
Generic available |
Yes |
No |
|
Common Side Effects |
Fast heart rate High blood pressure Headache |
Stomach pain Nausea/vomiting Diarrhea |
|
Average monthly cost |
$45-$50 |
$1,430 |
|
Duration of treatment |
Up to 12 weeks at a time |
Long-term weight management |
When setting out on a weight loss journey, consult with a healthcare professional to make sure that you are on the best path based on your health status and history.
Can You Take Wegovy and Phentermine Together?
There is currently no clear answer on whether it is safe to take Wegovy and phentermine together. Both medications have disclaimers on their prescribing information stating that their safety and efficacy have not been established when they are taken with other weight loss medications. Given the lack of research, it is best to discuss a treatment plan with your doctor and follow their instructions.
In Conclusion: Is Phentermine or Wegovy Better for Weight Loss?
While both medications can aid weight loss, Wegovy may help you lose more body weight.
Clinical trials on these medications have found that Wegovy may have an average weight loss that is about 3 times greater than the percentage of weight loss seen in phentermine trials. However, the Wegovy results are seen over a 16-month time span, whereas phentermine’s average weight loss of 3%-5% is after several months.
When your healthcare provider chooses the right medication for you, they also consider your medical history and lifestyle. Contact our medical professionals for personalized advice and receive a detailed weight loss plan tailored to your needs.
