Alli Vs. Phentermine: Drug Comparison

Alli^® (orlistat) is an over-the-counter (OTC) weight loss medication that works by inhibiting the enzyme lipase, which reduces the absorption of dietary fats in the intestines. Its FDA indication is for weight loss in adults who have overweight or obesity when used in conjunction with a reduced-calorie, low-fat diet. Alli is available in capsule form, typically taken with meals containing fat. Common side effects include gastrointestinal issues like oily stools, flatulence, and diarrhea, while serious concerns include malabsorption of fat-soluble vitamins. Alli should be used with caution in patients with liver disease or taking other medications that affect fat absorption, such as cyclosporine.

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

Alli (orlistat) is for:

• Weight loss in adults with overweight, 18 years and older, when used along with a reduced-calorie and low-fat diet

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 orally once daily and not more than three times daily

• Comes in 60 mg capsules

• Typically taken orally once daily

• Comes in 37.5 mg tablets

• Orlistat works by preventing the absorption of some of the fat you eat. The fat passes out of your body, so you may have bowel changes. You may get:

  • Gas with oily spotting

  • Loose stools

  • More frequent stools that may be hard to control

• Stop use and ask a doctor if:

  • You develop itching, yellow eyes or skin, dark urine or loss of appetite

  • Severe or continuous abdominal pain occurs

  • You are taking medicine for seizures and your seizures happen more often or get worse

Adverse events have been reported in the following systems:

• Cardiovascular

• Central nervous system

• Gastrointestinal

• Allergic

• Endocrine

• Do not use if you have had an organ transplant. Orlistat interferes with the medicines used to prevent transplant rejection

• Do not use if you are allergic to any of the ingredients in orlistat capsules

• Do not use if you are taking cyclosporine

• Do not use if you have been diagnosed with problems absorbing food

• Do not use if you are not overweight

• Drug interactions: anticoagulants, amiodarone, diabetes medicine, thyroid disease medicine, seizure medicine, antiretrovirals, other weight loss products

• 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

• Ask a doctor before use if you have ever had:

  • Gallbladder problems

  • Kidney stones

  • Pancreatitis

• Pregnancy: Do not use

• Breastfeeding: Do not use

• 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 Alli^® used by Haleon US Holdings LLC. See the full label for more complete information. Orlistat, the active ingredient in Alli, 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.