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Grapefruit adversely reacts with many prescription drugs. It can elevate the level of medication in your blood, increasing your risk for serious side effects. However, Synthroid, a brand-name thyroid replacement medication, does not interact dangerously with grapefruit, based on evidence available as of 2011. But new medical and drug interaction information could change this assessment. If you take Synthroid or any other medication, ask your doctor or pharmacist about updates on their interactions with grapefruit.
If you are experiencing serious medical symptoms, seek emergency treatment immediately.
No Known Interaction
MedlinePlus, a service of the National Institutes of Health, does not list grapefruit among its interaction warnings for Synthroid. According to the People’s Pharmacy, however, the majority of drugs remain untested for possible interactions with grapefruit.
CYP34A Enzyme Inhibition
The Side Effects of Lexapro & Grapefruit
Grapefruit reacts adversely with many medications because it inhibits your CYP34A enzyme from metabolizing drugs. Some drugs and some people are more sensitive to grapefruit's effect on this enzyme. If grapefruit slows the metabolism of a drug you take, you may end up with an excess of the medication in your system -- an overdose. An elevated dose of medication may increase the effectiveness of a medication and your risk for side effects.
- Grapefruit reacts adversely with many medications because it inhibits your CYP34A enzyme from metabolizing drugs.
- If grapefruit slows the metabolism of a drug you take, you may end up with an excess of the medication in your system -- an overdose.
Synthroid Uses and Side Effects
Synthroid treats a condition called hypothyroidism. Hypothyroidism develops when your body does not naturally produce enough of the thyroid hormone. Doctors may also prescribe Synthroid to treat goiter, a condition caused by an enlarged thyroid gland. Side effects of Synthroid include:
- weight loss
- hair loss
Theoretically, combining grapefruit with Synthroid could increase your risk for these symptoms. However, no evidence available as of 2011 suggests that it will.
- Synthroid treats a condition called hypothyroidism.
- Hypothyroidism develops when your body does not naturally produce enough of the thyroid hormone.
Known Drug Interactions
Grapefruit & Celexa
Drugs known to interact adversely with grapefruit include:
- oral contraceptives
- calcium channel blockers
- anti-anxiety medications
This is simply a partial list. For a full list of known drug interactions with grapefruit, consult a medical professional. Serious side effects include blood clots, gangrene, strokes and heart attacks .A single glass of grapefruit may slow your body's metabolism of a drug by 47 percent, according to the Harvard Medical School Family Health Guide.
The Side Effects of Lexapro & Grapefruit
Grapefruit & Celexa
Grapefruit's Effect on Thyroid Medication
Side Effects of Grapefruit Seed Extract
Does Grapefruit Juice Affect Ramipril?
Can You Eat a Grapefruit With Hydrochlorothiazide?
Can I Drink Grapefruit Juice With Wellbutrin?
Can I Take Benicar & Eat Grapefruit?
Can You Eat Grapefruit While Taking Crestor?
Does Drinking Grapefruit Juice Lower Blood Pressure?
- Medline Plus: Levothyroxine
- U.S. Food and Drug Administration: Synthroid
- “The New York Times”; Experts Reveal…Grapefruit Juice; Nicholas Bakalar; March 21 2006
- Grapefruit, raw, pink and red, all areas. USDA FoodData Central. Updated April 2019.
- Vitamin C - Fact Sheet for Health Professionals. National Institutes of Health (NIH). Office Of Dietary Supplements. Updated July 2019
- Chow O, Barbul A. Immunonutrition: Role in wound healing and tissue regeneration. Adv Wound Care (New Rochelle). 2014;3(1):46–53. doi:10.1089/wound.2012.0415
- Vitamin A Fact Sheet for Professionals. National Institutes of Health Office of Dietary Supplements. February 14, 2020
- Rasmussen HM, Johnson EJ. Nutrients for the aging eye. Clin Interv Aging. 2013;8:741–748. doi:10.2147/CIA.S45399
- Chen P, Zhang W, Wang X, Zhao K, Negi D, Zhou L, et al. Lycopene and risk of prostate cancer: A systematic review and meta-analysis. Medicine (Baltimore). 2015;94(33):e1260. doi:10.1097/MD.0000000000001260
- Vissers MCM, Das AB. Potential mechanisms of action for vitamin C in cancer: Reviewing the evidence. Front Physiol. 2018;9:809. doi:10.3389/fphys.2018.00809
- Dow CA, Going SB, Chow H-HS, Patil BS, Thomson CA. The effects of daily consumption of grapefruit on body weight, lipids, and blood pressure in healthy, overweight adults. Metabolism. 2012;61(7):1026-1035. doi:10.1016/j.metabol.2011.12.004
- Zhao CN, Meng X, Li Y, et al. Fruits for prevention and treatment of cardiovascular diseases. Nutrients. 2017;9(6):598. doi:10.3390/nu9060598
- Panche AN, Diwan AD, Chandra SR. Flavonoids: An overview. J Nutr Sci. 2016;5:e47. doi:10.1017/jns.2016.41
- Bourrier T, Pereira C. Allergy to citrus juice. Clin Transl Allergy. 2013;3(Suppl 3):P153. Published 2013 Jul 25. doi:10.1186/2045-7022-3-S3-P153
- Grapefruit Juice and Some Drugs Don't Mix. U.S. Food and Drug Administration. FDA Consumer Updates. Updated July 2017.
- Grapefruit juice and statins. Harvard Medical School - Healthbeat. Harvard Health Publishing. Updated September 2019.
- Bailey DG, Dresser G, Arnold JM. Grapefruit-medication interactions: Forbidden fruit or avoidable consequences?. CMAJ. 2013;185(4):309-16. doi:10.1503/cmaj.120951
- Kanellis A, Manganaris G. Fruit Ripening. (Nath P, Bouzayen M, Mattoo A, Pech J, eds.). Oxfordshire: CABI; 2014:110.
- Wanlapa S, Wachirasiri K, Sithisam-ang D, Suwannatup T. Potential of selected tropical fruit peels as dietary fiber in functional foods. International Journal of Food Properties. 2015;18(6):1306-1316. doi:10.1080/10942912.2010.535187
- Murphy MM, Barraj LM, Rampersaud GC. Consumption of grapefruit is associated with higher nutrient intakes and diet quality among adults, and more favorable anthropometrics in women, NHANES 2003-2008. Food Nutr Res. 2014;58:10.3402/fnr.v58.22179. doi:10.3402/fnr.v58.22179
Kathryn Gilhuly is a wellness coach based in San Diego. She helps doctors, nurses and other professionals implement lifestyle changes that focus on a healthy diet and exercise. Gilhuly holds a Master of Science in health, nutrition and exercise from North Dakota State University.