Phentermine vs. Mounjaro: Differences, similarities, and which one is better for you

In this article:

• Main differences
• Conditions treated
• Efficacy
• Coverage and cost
• Side effects
• Interactions
• Warnings
• FAQs

In this article

• Main differences
• Conditions treated
• Efficacy
• Coverage and cost
• Side effects
• Interactions
• Warnings
• FAQs

Many people may struggle with their weight-loss goals, which can be discouraging, especially if diet and exercise alone aren’t enough to manage weight. In some cases, a healthcare provider may recommend a weight loss drug like phentermine. However, if you experience weight challenges due to an underlying condition like Type 2 diabetes, you might consider a drug like Mounjaro. 

While phentermine and Mounjaro may help support weight management, they are very different medications. These medications differ in FDA-approved uses, how they work, dosage forms, and potential side effects. In addition, retail costs and insurance coverage can vary between the two. 

Read on to learn more about the similarities and differences between phentermine and Mounjaro. 

What are the main differences between phentermine and Mounjaro?

Phentermine and Mounjaro belong to different classes of medications. Phentermine, a generic drug approved in 1959, works as an anorectic or appetite suppressant. It is also classified as a stimulant that helps people feel less hungry, making them eat less. As a result, it directly helps promote weight loss.

Mounjaro is a brand-name drug approved in 2022 that contains the active ingredient tirzepatide. It works as a dual GIP and GLP-1 receptor agonist. Mounjaro helps the body produce more insulin when you eat and also makes you feel less hungry by affecting how your brain responds to food. It is used to improve blood sugar control in people with Type 2 diabetes. 

Phentermine is given as an oral medication once daily, while Mounjaro is given as a subcutaneous injection or injection under the skin. Phentermine is approved for use in people over 17 years old, while Mounjaro is approved for use in people aged 18 and older.

Main differences between phentermine and Mounjaro
	Phentermine	Mounjaro
Drug class	Anorectic Sympathomimetic  Stimulant	GIP and GLP-1 receptor agonist
Brand/generic status	Brand and generic available	Brand version only
What is the brand or generic name?	Brand name: Adipex-P, Lomaira, and others Generic name: Phentermine	Brand name: Mounjaro Generic name: Tirzepatide
What form(s) does the drug come in?	Oral tablet Oral capsule Orally disintegrating tablet	Subcutaneous injection
What is the standard dosage?	15 to 37.5 mg by mouth every morning before breakfast	2.5 mg injected under the skin once weekly for 4 weeks. Then, the dosage is increased to 5 mg once weekly.  The dosage may be increased in 2.5 mg increments after at least 4 weeks on the present dose up to a maximum of 15 mg once weekly, depending on the treatment response.
How long is the typical treatment?	Short-term use, up to 12 weeks at a time	Long-term
Who typically uses the medication?	Adults and children 17 and older	Adults 18 and older

Conditions treated by phentermine and Mounjaro

Phentermine is FDA-approved to support weight loss in people who are obese with a body mass index (BMI) of 30 or more. It is also approved to manage weight in people who are overweight with a BMI of 27 or more and a weight-related health condition like high blood pressure, high cholesterol, or diabetes. Phentermine is prescribed for short-term use and is often combined alongside regular exercise and a reduced-calorie diet.

Mounjaro is a newer drug FDA-approved to treat Type 2 diabetes. It is prescribed to help improve blood sugar levels when combined with diet and exercise. Because of its weight-loss effects, it may sometimes be prescribed off-label to support weight management in people with or without diabetes. However, it’s not approved for this use. The active ingredient in Mounjaro is available under the brand name Zepbound, which is approved for weight loss. 

Condition	Phentermine	Mounjaro
Obesity	Yes	Off-label
Excess weight with a weight-related condition	Yes	Off-label
Type 2 diabetes	No	Yes

Is phentermine or Mounjaro more effective?

Phentermine and Mounjaro are both effective medications. Phentermine, one of the oldest weight loss drugs, has been shown in studies to help individuals lose an average of approximately eight pounds (3.6 kg) over a 12-week period. Additionally, when combined with topiramate under the brand name Qsymia, phentermine can lead to around 10% weight loss at higher doses.

Mounjaro is approved to manage blood sugar levels, but studies have found that it also helps with weight loss. In people with Type 2 diabetes, tirzepatide led to an average weight loss of up to around 15%. It also lowered blood sugar levels (measured by HbA1c) by around 2%. In studies of people with obesity who do not have Type 2 diabetes, tirzepatide helped them lose more than 20% of their body weight on average.

While Mounjaro often leads to more pronounced weight loss, phentermine might be suitable for short-term goals. Still, other medications are available that are approved for Type 2 diabetes and weight loss. For example, Ozempic (semaglutide) and Rybelsus (semaglutide) are approved GLP-1 agonists for Type 2 diabetes. For weight loss, you might consider other medications like Saxenda (liraglutide), Contrave (naltrexone/bupropion), or Xenical (orlistat). 

The best treatment option will depend on your overall condition. Consult a healthcare provider for medical advice. 

Coverage and cost comparison of phentermine vs. Mounjaro

Phentermine is a generic medication that is usually cheaper than brand-name drugs. However, as a weight-loss drug, it is not usually covered by insurance plans and Medicare. Mounjaro, on the other hand, is a brand-name drug and tends to be more expensive out of pocket. However, it may be more likely than phentermine to be covered by insurance and Medicare plans. 

Depending on the quantity and strength of phentermine, the retail price can range from $27 to $100 per month. In contrast, Mounjaro has a higher retail cost, around $1,500 per package, and prices can change based on the quantity and location of the pharmacy.

For those looking to reduce their medication expenses, there are options to save on prescriptions. One way is using SingleCare coupons to help lower costs, especially for medications that aren’t fully covered by insurance.

	Phentermine	Mounjaro
Typically covered by insurance?	No	Yes
Typically covered by Medicare Part D?	No	Yes
Quantity	30, 37.5 mg tablets	4 prefilled injection pens
Typical Medicare copay	Varies	Varies
SingleCare cost	$10	$935

Common side effects of phentermine vs. Mounjaro

Phentermine and Mounjaro may share similar side effects like diarrhea and constipation. However, they largely differ in side effects due to how they work. 

In addition to diarrhea and constipation, phentermine is known to cause side effects that are common with stimulants, including insomnia, dizziness, euphoria, dry mouth, tremor, and changes in libido. It can also cause an increase in heart rate and blood pressure. 

The most common side effects of Mounjaro include gastrointestinal problems, including nausea, vomiting, indigestion, stomach pain, diarrhea, and constipation. These side effects are typically mild and temporary as the body gets used to the medication.

	Phentermine	Mounjaro
Side Effect	Applicable?	Applicable?
Insomnia	Yes	No
Dizziness	Yes	No
Euphoria	Yes	No
Tremor	Yes	No
Headache	Yes	No
Increased heart rate	Yes	Yes
High blood pressure	Yes	No
Dry mouth	Yes	No
Diarrhea	Yes	Yes
Constipation	Yes	Yes
Changes in libido	Yes	No
Nausea	No	Yes
Vomiting	No	Yes
Indigestion	No	Yes
Stomach pain	No	Yes

This may not be a complete list of adverse effects that can occur. Please refer to your doctor or healthcare provider to learn more.

Source: DailyMed (Phentermine), DailyMed (Mounjaro) 

Drug interactions of phentermine vs. Mounjaro

Phentermine should not be taken with monoamine oxidase inhibitors (MAOIs) or within 14 days of stopping them due to a risk of a severe increase in blood pressure. Mounjaro does not interact in the same way with MAOIs. However, MAOIs may decrease blood sugar levels in some people, which may increase the risk of low blood sugar or hypoglycemia while using Mounjaro. 

Phentermine may change how much insulin or other diabetes medications a person needs because it can lead to weight loss and improved insulin sensitivity. It can also make some blood pressure medications, like beta blockers, less effective.

Mounjaro may also increase the risk of low blood sugar when used with insulin or sulfonylureas, so doctors may need to adjust insulin doses when starting Mounjaro. In addition, Mounjaro can slow down how quickly the stomach empties, which might affect how well oral medications work. This can be important for medications like birth control pills or blood thinners, which may need adjustments. 

Drug	Drug Class	Phentermine	Mounjaro
Parnate (tranylcypromine) Nardil (phenelzine) Marplan (isocarboxazid)	MAOI	Yes	Yes
Lantus (insulin glargine) Levemir (insulin detemir) Humalog (insulin lispro) Novolog (insulin aspart)	Insulin	Yes	Yes
Glucotrol (glipizide) Amaryl (glimepiride)	Sulfonylureas	Yes	Yes
Prandin (repaglinide) Starlix (nateglinide)	Glinides	Yes	Yes
Inderal (propranolol) Tenormin (atenolol) Lopressor (metoprolol)	Beta-blocker	Yes	No

Consult a healthcare professional for other possible drug interactions 

Warnings of phentermine and Mounjaro

Phentermine is a controlled substance that can be addictive and is only meant for short-term use in weight loss. It also carries a risk of serious heart problems, including a rare lung condition called pulmonary hypertension and heart valve issues. Phentermine can also cause dizziness or affect alertness, so it’s important to be cautious when driving or using machinery.

Mounjaro may increase the risk of thyroid tumors, although this has only been seen in animal studies. People with a family history of thyroid cancer may need to avoid it. It can also cause pancreatitis, which leads to severe stomach pain, and may cause gallbladder problems, such as gallstones. Those with diabetic eye problems may need to use caution, as Mounjaro can temporarily worsen these conditions.

Both phentermine and Mounjaro should only be used under the guidance of a healthcare provider. Before using either, consult a healthcare provider for other potential warnings and precautions.

Frequently asked questions about phentermine vs. Mounjaro

What is Phentermine?

Phentermine is an oral medication used to help with weight loss. It works as an appetite suppressant, helping to reduce calorie intake. Phentermine is typically recommended for short-term use in combination with diet and exercise.

What is Mounjaro?

Mounjaro is an injectable medication used to manage blood glucose levels in people with Type 2 diabetes. It is not approved as a weight-loss medication, but some clinical trials have shown that it can support weight loss as a secondary benefit. Mounjaro is generally used as part of a long-term treatment plan for diabetes.

Are phentermine and Mounjaro the same?

No, phentermine and Mounjaro are not the same. Phentermine is specifically used for weight loss, while Mounjaro is used to manage blood sugar in people with Type 2 diabetes. They differ in approved uses, side effects, dosage forms, and cost. 

Is phentermine or Mounjaro better?

Both medications are effective. The more appropriate medication will depend on a person’s overall condition. Phentermine may be used for short-term weight loss goals, while Mounjaro may be better for long-term management of blood glucose levels in diabetes. However, Mounjaro has been shown to cause greater weight loss than phentermine. Consult a healthcare provider for medical advice. 

Can I use phentermine or Mounjaro while pregnant?

Neither phentermine nor Mounjaro is recommended for use during pregnancy. Both medications may carry risks to the developing fetus. Always consult your healthcare provider for advice on managing weight or diabetes during pregnancy.

Can I use phentermine or Mounjaro with alcohol?

It is generally advised to avoid alcohol while taking either phentermine or Mounjaro. Alcohol can interfere with the effectiveness of these medications and may increase the risk of side effects. Always consult your healthcare provider for advice regarding alcohol use while on prescription medications.