Mounjaro Vs. Phentermine: Drug Comparison

Mounjaro^® (tirzepatide) is an injectable medication used to treat type 2 diabetes by improving blood sugar control and promoting weight loss. It functions by activating two receptors, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which enhance insulin secretion and slow gastric emptying. Mounjaro is administered once weekly, with dose adjustments made based on the patient's response. Common side effects include nausea, diarrhea, and decreased appetite. It should be used with caution in individuals with a history of thyroid cancer or multiple endocrine neoplasia syndrome type 2​.

Phentermine is the active ingredient in brand-name medications including Adipex-P^®. The information below is about brand name Adipex-P. According to the FDA, “Generic medicines use the same active ingredients as brand-name medicines and work the same way, so they have the same risks and benefits as the brand-name medicines.”

Adipex-P (phentermine hydrochloride) is a prescription medication used as a short-term adjunct to weight loss in patients with obesity. It works as an appetite suppressant by stimulating the central nervous system, which increases heart rate and blood pressure while reducing hunger. Adipex-P is typically prescribed alongside a reduced-calorie diet and exercise regimen to enhance weight loss efforts. Common side effects include increased heart rate, dry mouth, insomnia, and nervousness. It is important to note that Adipex-P is intended for short-term use due to the potential for dependence and other adverse effects​.

Glucose-dependent insulinotropic polypeptide (GIP) receptor and glucagon-like peptide-1 (GLP-1) receptor agonist

Sympathomimetic amine anorectic

Mounjaro (tirzepatide) is indicated:

• As an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus

Adipex-P (phentermine hydrochloride) is indicated:

• As a short-term adjunct (a few weeks) in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction in the management of exogenous obesity for patients with an initial body mass index greater than or equal to 30 kg/m², or greater than or equal to 27 kg/m² in the presence of other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia)

• Typically taken as an injection once weekly

• Comes in 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg per 0.5 mL single-dose pens or single-dose vials

• Typically taken orally once daily

• Comes in 37.5 mg tablets

The most common adverse reactions, reported in ≥5% of patients treated with Mounjaro are:

• Nausea

• Diarrhea

• Decreased appetite

• Vomiting

• Constipation

• Indigestion

• Abdominal pain

Adverse events have been reported in the following systems:

• Cardiovascular

• Central nervous system

• Gastrointestinal

• Allergic

• Endocrine

• Personal or family history of medullary thyroid carcinoma or in patients with multiple endocrine neoplasia syndrome type 2

• Known serious hypersensitivity to tirzepatide or any of the excipients in Mounjaro

• Drug interactions: Mounjaro delays gastric emptying and has the potential to impact the absorption of concomitantly administered oral medications

• History of cardiovascular disease (e.g., coronary artery disease, stroke, arrhythmias, congestive heart failure, uncontrolled hypertension)

• During or within 14 days following the administration of monoamine oxidase inhibitors

• Hyperthyroidism

• Glaucoma

• Agitated states

• History of drug abuse

• Pregnancy

• Nursing

• Known hypersensitivity, or idiosyncrasy to the sympathomimetic amines

• Drug interactions: Monoamine oxidase inhibitors, alcohol, insulin and oral hypoglycemics, adrenergic neuron blocking drugs

• Pancreatitis

• Low blood sugar with concomitant use of insulin secretagogues or insulin

• Hypersensitivity reactions

• Acute kidney injury

• Severe gastrointestinal disease

• Diabetic retinopathy complications in patients with a history of diabetic retinopathy

• Acute gallbladder disease

• Pregnancy: Based on animal study, may cause fetal harm

• Females of reproductive potential: Females using oral contraceptives should consider switching to a non-oral contraceptive method or add a barrier method of contraception for 4 weeks after initiation and for 4 weeks after each dose escalation

• Coadministration with other drugs for weight loss is not recommended

• Rare cases of primary pulmonary hypertension have been reported

• Rare cases of serious regurgitant cardiac valvular disease have been reported

• Tolerance to the anorectic effect usually develops within a few weeks

• Adipex-P may impair the ability of the patient to engage in potentially hazardous activities such as operating machinery or driving a motor vehicle

• Risk of abuse and dependence

• Concomitant alcohol use may result in an adverse drug reaction

• Use caution in patients with even mild high blood pressure

• A reduction in dose of insulin or oral hypoglycemic medication may be required in some patients

• Breastfeeding: Discontinue drug or nursing taking into consideration importance of drug to mother

WARNING: RISK OF THYROID C-CELL TUMORS

Tirzepatide causes thyroid C-cell tumors in rats. It is unknown whether Mounjaro causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans as the human relevance of tirzepatide-induced rodent thyroid C-cell tumors has not been determined.

Mounjaro is contraindicated in patients with a personal or family history of MTC or in patients with multiple endocrine neoplasia syndrome type 2 (MEN 2). Counsel patients regarding the potential risk of MTC and symptoms of thyroid tumors.

*This information is from the label for brand name Mounjaro. See the Full Prescribing Information for more complete information. Tirzepatide, the active ingredient in Mounjaro, may also be the active ingredient in other medications, and this information may not be accurate for all medications that include the active ingredient tirzepatide.

*This information is from the label for brand name Adipex-P^®. See the Full Prescribing Information for more complete information. Phentermine, the active ingredient in Adipex-P, may also be the active ingredient in other medications, and this information may not be accurate for all medications that include the active ingredient phentermine.