Soy

Are there any interactions with medications?

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Medications for depression (MAOIs)
Interaction Rating: Major Do not take this combination.

Fermented soy products such as tofu and soy sauce contain tyramine. Tyramine is an amino acid that is involved in blood pressure regulation. Tyramine is broken down by monoamine oxidase. Some medications for depression (MAOIs) can decrease the breakdown of tyramine. Consuming more than 6 mg of tyramine while taking one of these medications can increase the risk of serious side effects such as blood pressure getting too high. The amount of tyramine in fermented soy products is usually small, often less than 0.6 mg per serving; however, there can be variation depending on the specific product used, storage conditions, and length of storage. Storing one brand of tofu for a week can increase tyramine content from 0.23 mg to 4.8 mg per serving. If you take one of these medications, avoid fermented soy products that contain high amounts of tyramine.

Some of these medications include phenelzine (Nardil), tranylcypromine (Parnate), and others.

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Antibiotic drugs
Interaction Rating: Moderate Be cautious with this combination.
Talk with your health provider.

Antibiotics are used to reduce harmful bacteria in the body. Antibiotics can also reduce friendly bacteria in the intestines. Friendly bacteria in the intestines seem to help increase the effectiveness of soy. By reducing the number of bacteria in intestines, antibiotics might decrease the effectiveness of soy. But it is too soon to know if this interaction is a big concern.

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Estrogens
Interaction Rating: Moderate Be cautious with this combination.
Talk with your health provider.

Large amounts of soy might have some of the same effects as estrogen. But soy isn't as strong as estrogen pills. Taking soy along with estrogen pills might decrease the effects of estrogen pills.

Some estrogen pills include conjugated equine estrogens (Premarin), ethinyl estradiol, estradiol, and others.

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Tamoxifen (Nolvadex)
Interaction Rating: Moderate Be cautious with this combination.
Talk with your health provider.

Some types of cancer are affected by hormones in the body. Estrogen-sensitive cancers are cancers that are affected by estrogen levels in the body. Tamoxifen (Nolvadex) is used to help treat and prevent these types of cancer. Soy seems to also affect estrogen levels in the body. By affecting estrogen in the body, soy might decrease the effectiveness of tamoxifen (Nolvadex). Do not take soy if you are taking tamoxifen (Nolvadex).

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Warfarin (Coumadin)
Interaction Rating: Moderate Be cautious with this combination.
Talk with your health provider.

Warfarin (Coumadin) is used to slow blood clotting. Soy has been reported to decrease the effectiveness of warfarin (Coumadin). Decreasing the effectiveness of warfarin (Coumadin) might increase the risk of clotting. It is unclear why this interaction might occur. Be sure to have your blood checked regularly. The dose of your warfarin (Coumadin) might need to be changed.

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Medications changed by the liver (Cytochrome P450 2C9 (CYP 2C9) substrates)
Interaction Rating: Minor Be cautious with this combination.
Talk with your health provider.

Some medications are changed and broken down by the liver. Soy might increase how quickly the liver breaks down some medications. But it is too soon to know if this interaction occurs in all people or if it affects how well the medication works.

Some medications changed by the liver include carvedilol (Coreg), fluvastatin (Lescol), losartan (Cozaar), phenytoin (Dilantin), and many others.

Dosing considerations for Soy.

The following doses have been studied in scientific research:

BY MOUTH:

• For high cholesterol: 20-50 grams per day of soy protein.
• For preventing weak bones (osteoporosis): 40 grams per day soy protein containing 2-2.25 mg isoflavones per gram.
• For menopausal symptoms such as hot flashes:
• 20-60 grams per day of soy protein providing 34-76 mg isoflavones.
• concentrated soy isoflavone extracts providing 50-120 mg/day of isoflavones.
• Genistein, a soy isoflavone: 54 mg per day.

• For protein in the urine of people with kidney disease: a diet limited to 700-800 mg/kg soy protein daily has been used.
• For diarrhea in infants, soy fiber fortified formula containing 18-20 grams of soy protein per liter.
• For type 2 diabetes, touchi extract 300 mg three times daily. Touchi is a traditional Chinese food prepared from soybeans.
• For type 2 diabetes in postmenopausal women, 30 grams of soy protein daily, containing 132 mg of phytoestrogens daily for up to 12 weeks.

Soy foods contain variable amounts of isoflavones. Soy flour contains 2.6 mg isoflavones per gram of soy flour, fermented soybeans contain 1.3 mg per gram, boiled soybeans contain 0.6 mg per gram, soymilk contains 0.4 mg per gram, soybean curd contains 0.5 mg per gram, fried soybean curd contains 0.7 mg per gram, soybean paste contains 0.4 mg per gram, and soy sauce contains 0.016 mg per gram.