Orlistat Vs. Phentermine: Drug Comparison

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

Xenical (orlistat) is a prescription medication used for weight management by inhibiting the enzyme lipase, which reduces the absorption of dietary fats in the intestines, thereby helping with weight loss. Its FDA-approved indication is for obesity management, including weight loss and weight maintenance, in conjunction with a reduced-calorie diet. Xenical is available in capsule form and is typically taken three times daily with meals containing fat. Common side effects include gastrointestinal issues such as oily stools, flatulence, and frequent bowel movements, especially after consuming high-fat meals. Xenical can affect the absorption of fat-soluble vitamins, and patients are advised to take a multivitamin supplement to avoid deficiencies.

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​.

Reversible inhibitor of gastrointestinal lipases

Sympathomimetic amine anorectic

Xenical (orlistat) is indicated:

• For obesity management including weight loss and weight maintenance when used in conjunction with a reduced-calorie diet

• To reduce the risk for weight regain after prior weight loss

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 three times daily

• Comes in 120 mg capsules

• Typically taken orally once daily

• Comes in 37.5 mg tablets

Most common treatment emergent adverse reactions (≥5% and at least twice that of placebo) include:

• Oily spotting

• Flatus with discharge

• Fecal urgency

• Fatty/Oily stool

• Oily evacuation

• Increased defecation

• Fecal incontinence

Adverse events have been reported in the following systems:

• Cardiovascular

• Central nervous system

• Gastrointestinal

• Allergic

• Endocrine

• Pregnancy

• Chronic malabsorption syndrome

• Cholestasis

• Known hypersensitivity to Xenical or to any component of this product

• Drug interactions: cyclosporine, fat-soluble vitamin supplements and analogues, levothyroxine, warfarin, amiodarone, antiepileptic drugs, antiretroviral drugs

• 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

• Xenical has drug interactions and can decrease vitamin absorption

• Take a multivitamin supplement that contains fat-soluble vitamins to ensure adequate nutrition

• Rare cases of severe liver injury with hepatocellular necrosis or acute hepatic failure have been reported

• Patients may develop oxalate nephrolithiasis and oxalate nephropathy following treatment with Xenical

• Substantial weight loss can increase the risk of cholelithiasis

• Exclude organic causes of obesity (e.g., hypothyroidism) before prescribing Xenical

• Gastrointestinal events may increase when Xenical is taken with a diet high in fat (>30% total daily calories from fat)

• Breastfeeding: Caution should be exercised when administered to a nursing woman

• 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

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

*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.