Phentermine Vs. Tirzepatide: Drug Comparison

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​.

Tirzepatide is the active ingredient in the brand-name medication Zepbound^®. The information below is about brand name Zepbound. 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.”

Zepbound (tirzepatide) is an injectable medication approved by the FDA for chronic weight management in adults with obesity or overweight who have at least one weight-related condition. It works by activating both glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) hormone receptors, which help reduce appetite and food intake. It is taken once a week as an injection and is gradually increased over time to achieve effective weight loss results. Common side effects include nausea, diarrhea, constipation, and abdominal pain, with more serious risks like thyroid tumors and pancreatitis necessitating careful patient screening. This medication should be used alongside a reduced-calorie diet and increased physical activity for best results.

Sympathomimetic amine anorectic

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

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)

Zepbound (tirzepatide) is indicated:

• As an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in adults with an initial body mass index (BMI) of:

  • 30 kg/m² or greater (obesity) or

  • 27 kg/m² or greater (overweight) in the presence of at least one weight-related comorbid condition (e.g., hypertension, dyslipidemia, type 2 diabetes mellitus, obstructive sleep apnea or cardiovascular disease)

• Typically taken orally once daily

• Comes in 37.5 mg tablets

• 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

Adverse events have been reported in the following systems:

• Cardiovascular

• Central nervous system

• Gastrointestinal

• Allergic

• Endocrine

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

• Nausea

• Diarrhea

• Vomiting

• Constipation

• Abdominal pain

• Indigestion

• Injection site reactions

• Fatigue

• Hypersensitivity reactions

• Belching

• Hair loss

• Gastroesophageal reflux disease (heartburn)

• 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

• 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 Zepbound

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

• 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

• Severe gastrointestinal disease

• Acute kidney injury

• Acute gallbladder disease

• Acute pancreatitis

• Hypersensitivity reactions

• Low blood sugar: Concomitant use with an insulin secretagogue or insulin may increase the risk of low blood sugar, including severe low blood sugar

• Diabetic retinopathy complications in patients with type 2 diabetes mellitus

• Suicidal behavior and ideation

• Pregnancy: May cause fetal harm. When pregnancy is recognized, discontinue Zepbound

• 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

WARNING: RISK OF THYROID C-CELL TUMORS

In rats, tirzepatide causes thyroid C-cell tumors. It is unknown whether Zepbound 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.

Zepbound 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 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.

*This information is from the label for brand name Zepbound^®. See the Full Prescribing Information for more complete information. Tirzepatide, the active ingredient in Zepbound, 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.