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Alli 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), whereas 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

 

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Phentermine

(Adipex-P)

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Summary for Alli

Prescription or over-the-counter

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).

Indications for Alli

Xenical (orlistat):

  • Obesty management in adults with a body mass index (BMI) of:
    • 30 kg/m2 or greater or
    • 27 kg/m2 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

Pros and Cons for Alli

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

Common Side Effects for Alli

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

Warnings for Alli

  • Medication interactions
  • Liver injury
  • Higher oxalate levels in the urine
  • Gallstones
  • Other causes of obesity

Summary for Phentermine

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 for Phentermine

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

Pros and Cons for Phentermine

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 for Phentermine

  • Dry mouth
  • Headache
  • Tremor
  • Constipation
  • Diarrhea
  • High blood pressure
  • Fast heart rate
  • Difficulty sleeping

Warnings for Phentermine

  • 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 Alli vs. Phentermine

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Alli90 capsules / 60mg
$49.67$65.30
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Phentermine30 tablets / 37.5mg
$12.05-
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