Updated April 30, 2009.

The only FDA-approved over-the-counter weight loss drug is Alli -- which is the brand name for the medication orlistat. (Orlistat in higher dosages is also available by prescription under the brand name Xenical.) Orlistat is a fat-blocking drug, taken with meals to help block some of the fat -- and therefore calories -- from meals, as an aid in losing weight.

In late March, 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 will now include 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 4 hours apart and to perform regular evaluations of thyroid function.

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

• Under "Drug Interactions," they have added "Hypothyroidism has been reported in patients treated concomitantly with orlistat and levothyroxine"
• Under "Adverse Reactions / Other Clinical Studies or Postmarketing Surveillance," they have added, "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 Alli or Xenical 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 a dosage adjustment of your thyroid medication.About Mary Shomon | Thyroid Forum | Twitter | Facebook
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