3D image human with thyroid with text overlay for Clarinex


Clarinex (desloratadine), a prescription antihistamine, is considered safe to take if you have thyroid disease.

There haven't been any studies that have suggested that Clarinex, or antihistamines in general, are dangerous if you have some sort of thyroid dysfunction.[1]

Additionally, the prescribing information for Clarinex does not list thyroid disease as a contraindication, or even a precaution, for use.[2]

There is some concern with using antihistamines like Clarinex if you have low thyroid levels (hypothyroidism) however due to the risk of additive sedative effects.

One of the more well-known symptoms of hypothyroidism is a feeling of tiredness, lethargy, and fatigue. Therefore, the use of antihistamines, especially sedating ones like Zyrtec, could cause you to feel more tired than usual in you already have low thyroid levels.

Fortunately, Clarinex is essentially non-drowsy. The vast majority of individuals do not experience tiredness or sedation as a side effect of the drug and it would be a good choice of antihistamine if you do want to avoid sedative effects.[3]


It is important to note that Clarinex RediTabs, which are disintegrating tablets, do contain aspartame. Some studies have suggested that aspartame can cause decreases in thyroid hormone levels.[4]

More data is needed to make a definitive conclusion on how aspartame could affect those with thyroid disease, but if you are looking to avoid any potential complication, you should stick with regular Clarinex tablets and not use the disintegrating formulation.

About Clarinex

Clarinex (desloratadine) is a non-sedating second-generation antihistamine that is available only by prescription.

It is the active metabolite of Claritin (loratadine) and studies show that desloratadine is more potent on an mg to mg basis than loratadine and may have less risk of certain side effects (like QT prolongation).[5]

Clarinex is dosed once-daily and can be given with or without food.


Clarinex isn't known to have any negative effects on the thyorid. It is considered safe to take in those with thyroid disease. However, Claritin RediTabs contain aspartame, which studies suggest may influence thyroid function.

  2. ^ Clarinex Prescribing Information. AccessFDA
  3. ^ Desloratadine: A new, nonsedating, oral antihistamine. PubMed
  4. ^ Autoimmune Thyroiditis with Hypothyroidism Induced by Sugar Substitutes. PubMed
  5. ^ Elsevier ClinicalKey: Clarinex Monograph. ClinicalKey