Alli/Xenical/Orlistat, Weight Loss, and Your Thyroid

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Alli is the brand name of a reduced strength over-the-counter version of the brand name prescription drug Xenical (known generically as orlistat).

Orlistat is designed for people 18 years of age and older who are overweight, and have a BMI (body mass index) of 30 or more (obese), or 27-29 (overweight) and have other high-risk health factors.

Orlistat works by blocking the enzyme that digests fat in your intestines.

The drug only works on your intestines and is designed to reduce about 25% of the fat calories you consume.

Orlistat is designed to be used in conjunction with regular physical activity and a low calorie/low-fat diet. No more than 30 percent of calories from each meal should come from fat, this will help reduce stomach bloating and other unpleasant side effects. Diets high in fat combined with orlistat can cause stomach bloating and extreme diarrhea.

Orlistat can be somewhat effective for weight loss for some people. The manufacturer claims that when used in conjunction with a reduced calorie/low-fat diet, adults can lose about 50 percent more weight—essentially, for every two pounds you lose, you would lose a third-pound using orlistat.

Some studies, however, have shown that when it works, orlistat results in around 8 pounds more weight loss in a year, compared to placebo. Most people also tend to regain the weight in the year after taking the drug.

Another study found that a low-carbohydrate diet was just as effective as the combination of orlistat and a low-fat diet.

Interactions and Warnings

Orlistat can have interactions for patients with the following conditions. If you have any of these health problems, you need to discuss the use of orlistat with your physician, before starting:

You should NOT take orlistat if you:

  • Are already at a healthy weight
  • Are pregnant or breastfeeding
  • Have issues with food absorption
  • Have had an organ transplant, and/or take Neoral, Sandimmune, Cyclosporine, and other immunosuppressant medicines

Side Effects

One of the chief drawbacks of orlistat are the side effects, which can include:

  • Oily stools
  • More frequent bowel movements
  • Hard to control bowel movements
  • Abdominal pain/discomfort
  • Oily discharge from anus
  • Oily spots on undergarments
  • Gas with oily anal discharge
  • Headache
  • Back pain
  • Upper respiratory infection
  • Rectal pain
  • Anxiety
  • Changes in menstrual cycle

Rare and more dangerous side effects can suggest liver damage. Call your doctor immediately if you experience any of these symptoms while taking orlistat:

  • Dark urine
  • Fever
  • Jaundiced skin or eyes
  • Light colored stools
  • Loss of appetite
  • Hives, persistent itching
  • Severe fatigue
  • Weakness
  • Vomiting

In the rare event of severe side effects—which can include difficulty swallowing, difficulty breathing, uncontrollable itching/hives, or severe stomach/abdominal pain—you should call 911 or seek care immediately.

Orlistat and Your Thyroid

In 2009, the FDA approved safety labeling revisions for levothyroxine sodium tablets (i.e., Synthroid, Levoxyl, etc.) to advise of drug interactions with orlistat.

Levothyroxine's prescribing information includes a warning that indicates that use of orlistat may decrease levothyroxine absorption and lead to hypothyroidism and that clinicians are advised to administer levothyroxine and orlistat at least four hours apart and to perform regular evaluations of thyroid function.

Xenical's prescribing information has been revised to reflect the potential interaction between orlistat and levothyroxine. Specifically:

  • Under "Drug Interactions," it states "Hypothyroidism has been reported in patients treated concomitantly with orlistat and levothyroxine"
  • Under "Adverse Reactions/Other Clinical Studies or Postmarketing Surveillance," it states: "Hypothyroidism has been reported in patients treated concomitantly with orlistat and levothyroxine."
  • Under "Can I take XENICAL while taking other medications?" they have added "XENICAL and levothyroxine should be taken at least 4 hours apart"

Bottom Line

If you're a thyroid patient trying to lose weight—as many are—keep in mind that orlistat may affect absorption of your thyroid medication, and make you more hypothyroid.

Take your thyroid medication at least 4 hours apart from your Alli or Xenical. And have your thyroid evaluated more frequently while you're taking the medication, to make sure you don't need to adjust the dosage of your thyroid medication to account for decreased absorption.