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Compare Orlistat vs. Phentermine

Head-to-head comparisons of medication uses, side effects, warnings, and more.

Key takeaways

Orlistat (Alli, Xenical) and phentermine (Adipex-P) are both medications used to help with weight loss, but they work in different ways and belong to different medication classes. Orlistat is a lipase inhibitor that helps your body absorb less fat from the food you eat, while phentermine is a sympathomimetic that suppresses your appetite. Orlistat is available both over-the-counter (as Alli) and by prescription (as Xenical), whereas phentermine is a prescription-only medication and is a controlled substance due to its potential for misuse. Orlistat is taken three times a day with meals containing fat, while phentermine is usually taken once a day in the morning. Common side effects of orlistat include oily spotting and gas with anal discharge, while phentermine can cause dry mouth and trouble sleeping. Orlistat can interact with medications like levothyroxine (Synthroid, Levoxyl, Tirosint) and warfarin (Coumadin, Jantoven), and phentermine should not be combined with other weight loss medications or alcohol. Additionally, orlistat is not recommended for those with chronic malabsorption syndrome, while phentermine is not recommended for people with heart problems.

  • Orlistat
    Phentermine (Adipex-P)
  • Orlistat
    Phentermine (Adipex-P)

  • Summary of Orlistat vs. Phentermine

    Summary for Lipase inhibitor

    Orlistat is a medication that works alongside diet and exercise to increase weight loss in people who are overweight or obese. It needs to be taken three times a day and is available with a prescription in a higher dose (Xenical) or over the counter in a lower dose (Alli).

    Summary for Sympathomimetic
    Prescription only

    Phentermine (Adipex-P) is an appetite suppressant. It's a prescription weight loss pill for people ages 17 years and older. This medication works best when it's part of a treatment plan that involves healthy diet and regular exercise. Phentermine (Adipex-P) is taken by mouth once daily, typically in the morning. Some of the more common side effects of this medication include dry mouth, trouble sleeping, and headache.

  • Indications of Orlistat vs. Phentermine

    Indications for

    Xenical (orlistat):

    •Obesty management in adults with a body mass index (BMI) of:
    •30 kg/m^2^ or greater or
    •27 kg/m^2^ or greater and at least one weight-related condition (e.g., high blood pressure, type 2 diabetes, or high cholesterol)

    Alli (orlistat):

    •Weight loss in adults when combined with a lower-calorie and low-fat diet
    Indications for

    Short-term treatment for weight management in adults with a body mass index (BMI) of:

    •30 kg/m2 or greater; or
    •27 kg/m2 or greater, and with at least one other weight-related condition (e.g., high blood pressure, high blood sugar, high cholesterol)

  • Pros and Cons of Orlistat vs. Phentermine

    Pros and Const for Lipase inhibitor
    Pros
    •Works well to block a portion of the fat you eat
    •Xenical is approved for people ages 12 years and older.
    •Available in both prescription and over-the-counter forms
    Cons
    •Still need to maintain a healthy diet and exercise routine
    •Must remember to take with each fat-containing meal
    •Only available as a brand medication so it can be expensive
    Pros and Const for Sympathomimetic
    Pros
    •Can help you lose 5% to 10% of body weight
    •Usually taken by mouth once per day
    •Available as a lower-cost generic
    •Comes as tablets, capsules, and orally disintegrating tablets
    Cons
    •Most insurance companies don't cover the cost of phentermine (Adipex-P).
    •Has a risk of misuse and dependence since it's a stimulant medication that's similar to amphetamines
    •Might not be a good choice for people with high blood pressure
    •Should be avoided in children 16 years of age and younger, pregnant and breastfeeding women, and people with serious heart problems

  • Common Side Effects of Orlistat vs. Phentermine

    Common Side Effects for

    Xenical (orlistat):

    •Oily spotting on underwear (4-27%)
    •Gas with anal discharge (2-24%)
    •Urge to have a bowel movement (3-22%)
    •Fatty or oily stool (6-20%)
    •Having more bowel movements (3-11%)
    •Difficulty controlling bowel movements (2-8%)

    Alli (orlistat):

    •Gas with oily spotting
    •Loose stools
    •More frequent stools that are hard to control
    Common Side Effects for
    •Dry mouth
    •Headache
    •Tremor
    •Constipation
    •Diarrhea
    •High blood pressure
    •Fast heart rate
    •Difficulty sleeping

  • Warnings of Orlistat vs. Phentermine

    Common Side Effects for
    •Medication interactions
    •Liver injury
    •Higher oxalate levels in the urine
    •Gallstones
    •Other causes of obesity
    Common Side Effects for
    •Not safe to combined with other weight loss medications
    •Phentermine not working well
    •Risk of misuse and dependence
    •Trouble concentrating or problem with coordination
    •Heart and lung problems
    •Risk of high blood pressure
    •Risk of low blood sugar in people with diabetes

  • Prices with our coupons for Orlistat vs. Phentermine

    Learn more about Orlistat
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