Synthroid is a brand name for the prescription drug levothyroxine, which replaces the T4 thyroid hormone for patients with hypothyroidism. Sythroid must be taken orally every day, preferably at the same time each day, and may need to be taken for the rest of your life. Because Synthroid dissolves in your intestines, taking diet pills may interfere with that process, blocking the absorption of your replacement thyroid hormone. Certain foods and minerals can also affect the way your body absorbs Synthroid, so you should check with your doctor before taking any type of over-the-counter supplements, vitamins or herbal remedies.
Possible Interactions
Anything that interferes with digestion could possibly affect the absorption of Synthroid. A diet high in insoluble fiber -- the kind of fiber that adds bulk to help pass digested food through your intestines -- can change the effectiveness of your hormone replacement. Walnuts and soy isoflavones can also affect absorption of Synthroid. Calcium and iron can decrease the potency of the drug, and medications containing these minerals should not be taken at the same time as Synthroid.
Orlistat
Orlistat, the only FDA-approved over-the-counter weight loss drug, is not recommended for use with Synthroid. Sold under the brand name Alli, orlistat works by blocking the absorption of fat in your intestines. Synthroid may not be absorbed if you take it together with Alli. Mayo Clinic notes that Alli should only be taken at least four hours before or four hours after Synthroid to ensure proper hormone assimilation.
Diabetes Weight-Loss Medications
Metformin, also sold as Glucophage, is a diabetes medication that helps lower blood sugar levels. Because Glucophage increases insulin sensitivity, it can reduce appetite and help you eat fewer calories, resulting in weight loss. Its also prescribed for overweight patients without diabetes. Unlike Alli, which hinders Synthroid absorption, it's actually the Synthroid that stops Glucophage from working effectively. Byetta, another diabetes medication prescribed for weight loss, works by slowing digestion and keeping food in your stomach for a longer period of time. Anything that interferes with normal digestion can affect the way your body processes Synthroid. If you have diabetes, you must check you glucose levels often; Synthroid can affect blood sugar.
Metabolism and Weight Loss
Hypothyroidism slows your metabolism, and weight gain is a common side effect. Although frustrating, you will have an easier time losing weight once you've found your proper dose of Synthroid. It can take three months or more for thyroid hormone levels to regulate and boost your metabolism. Instead of relying on diet pills to lose weight, try raising your metabolism by exercising regularly. Strength training exercises that build lean muscle mass can help keep your metabolism high because muscle tissue needs more calories than fat, even at rest.
References
- PubMed Health; Hypothyroidism; April 2010
- MayoClinic.com; Levothyroxine (Oral Route) -- Precautions; November 2010
- eMedTV; Synthroid; Kristi Monson, PharmD; June 2008
- Drugs.com: Drug Interactions Between Glucophage and Synthroid
- RedBook: Do Diet Pills Really Work? - Metformin
- Drugs.com: Drug Interactions Between Alli and Synthroid
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