Synthroid is a brand name for the medication levothyroxine, a treatment for hypothyroidism. If your thyroid gland is not producing enough thyroid hormone, a doctor may prescribe Synthroid, which is a synthetic version of human thyroid hormone. Certain foods and dietary supplements block your body's absorption of Synthroid, and you should avoid these for several hours after taking the medication. Rhubarb is not on the list of forbidden foods, but it may be wise to avoid consuming rhubarb and Synthroid at the same time.
T4 Blockers
Synthroid is a form of the T4 thyroid hormone. Your body absorbs T4 best on an empty stomach, and certain foods decrease its absorption. These include soybean flour, infant formula, cottonseed meal, walnuts and foods rich in dietary fiber or calcium. Calcium carbonate supplements are especially strong T4 blockers. If you need supplemental calcium, your doctor will instruct you on how to take it safely. Don't avoid T4-blocking foods entirely, but schedule them several hours from your medication. For instance, if you take Synthroid in the morning, wait until at least midday to drink milk, eat a bran muffin or snack on walnuts.
Rhubarb
Rhubarb is high in both dietary fiber and calcium. A 1-cup serving of cooked, sweetened rhubarb contains 348 milligrams of calcium, more than a third of the recommended daily value for this mineral. A serving also contains 4.8 grams of dietary fiber, about 20 percent of the daily value. Since dietary fiber and calcium can both decrease Synthroid absorption, avoid rhubarb for a few hours after taking it. However, occasionally eating rhubarb close to your Synthroid dose is unlikely to harm you.
Oxalic Acid
Though rhubarb is especially high in calcium, it also contains oxalic acid, a substance that blocks calcium absorption. Spinach also contains oxalic acid. The calcium in rhubarb isn't readily available to your body, though it may still interfere with Synthroid absorption. Don't rely on rhubarb to meet your daily calcium needs. Instead, choose other dietary sources of calcium, such as dairy products, leafy green vegetables and tofu, and eat them at meals that don't follow your Synthroid dose.
Considerations
Numerous drugs and dietary supplements interact poorly with Synthroid. Iron supplements, antacids, seaweed or other high-iodine foods, antidepressants and cholesterol medications all may pose problems. Provide your prescribing doctor with a complete list of medications and supplements, and discuss dietary strategies for getting the most out of Synthroid therapy.
References
- Drugs.com: Synthroid
- Drugs.com: Synthroid (Levothyroxine) Alcohol & Food Interactions
- U.S. Food and Drug Administration Nutrient Data Laboratory: Search the USDA National Nutrient Database
- Oregon State University Linus Pauling Institute: Calcium
- MayoClinic.com: What Does Percent Daily Value Mean on Food Labels?
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