Grapefruit - Armour Thyroid (Levothyroxine, Liothyronine) Interaction
Herbal: Grapefruit
Also Known As: Citrus paradisi
Drug: Levothyroxine, Liothyronine
Brand names:
Armour Thyroid
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Apr 20, 2025
Interaction Details
Levothyroxine, Liothyronine is classified as belonging to the following category: Levothyroxine (Synthroid, Others)
Grapefruit juice can decrease blood levels of levothyroxine, potentially decreasing the effectiveness of levothyroxine.
Clinical research shows that grapefruit juice modestly decreases levothyroxine levels by 11% by inhibiting organic anion transporting polypeptide (OATP). Grapefruit juice is thought to affect OATP for only a short time. Therefore, separating drug administration and consumption of grapefruit by at least 4 hours is likely to prevent this interaction.
Interaction Rating
Likelihood of Occurrence
PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
References
- Greenblatt DJ. Analysis of drug interactions involving fruit beverages and organic anion-transporting polypeptides. J Clin Pharmacol 2009;49:1403-7.
- Bailey DG. Fruit juice inhibition of uptake transport: a new type of food-drug interaction. Br J Clin Pharmacol 2010;70:645-55.
- Lilja, J. J., Laitinen, K., and Neuvonen, P. J. Effects of grapefruit juice on the absorption of levothyroxine. Br J Clin Pharmacol 2005;60(3):337-341.
Grapefruit Overview
Grapefruit is a tropical citrus fruit known for its tart and tangy flavor. They are a good source of vitamin C and other nutrients, including vitamin A, potassium, and fiber.
There are several varieties of grapefruits, including white, pink, and red. This color difference is mostly attributed to their respective lycopene content. White grapefruits are the most common and have a slightly bitter taste. Pink and red grapefruits are sweeter and have a more complex flavor.
Grapefruit and grapefruit seed extract is commonly used in dietary supplements for a variety of conditions, such as yeast infections, urinary tract infections, and respiratory infections. It is also sometimes used to treat digestive problems, such as diarrhea and indigestion.
Drug interactions with grapefruit are quite prevalent and if you take prescription medication, you should talk with your doctor or pharmacist first before consuming grapefruit.
Grapefruit - More Interactions
Grapefruit interacts with 961 drugs
Interaction Rating Key
These severity listings are for informational use only. Never start, stop or otherwise change your therapy before speaking with your provider.
| Major | The combined use of these agents is strongly discouraged as serious side effects or other negative outcomes could occur. |
| Moderate | Use cautiously under the care of a healthcare professional or avoid this combination. A significant interaction or negative outcome could occur. |
| Minor | Be aware that there is a chance of an interaction. Watch for warning signs of a potential interaction. |
| Unknown | No interactions have been reported or no interaction data is currently available. |
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Parts of this content are provided by the Therapeutic Research Center, LLC.
DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.
© 2021 Therapeutic Research Center, LLC
Drug descriptions are provided by MedlinePlus.
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In addition to being a clinical pharmacist specializing in pharmacotherapy, Dr. Brian Staiger is a registered herbalist through the American Herbalist Guild. He has combined his passion for pharmacy practice with the study of medical ethnobotany to improve patient care. Feel free to reach out about any of your herbal or medication questions!
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