The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.


Avoid with a known allergy to soy, any of its parts, or members of its plant family.

Soy may act as a food allergen similar to milk, eggs, peanuts, fish, and wheat. Symptoms of an allergic reaction range from a runny nose, to inflammation of the digestive tract to a sudden drop in blood pressure.

Side Effects and Warnings

Soy is likely safe when used in the diet in adults, children, and infants, although maximum duration is unknown. Soy protein has been safely used for up to one year. Soy formula has been safely used in full-term infants.

Soy may cause atopic eczema (skin problems), asthma, bad taste, bleeding, bloating, constipation, damage to pancreas, diarrhea, goiters (enlarged neck due to increased thyroid size), growth failure, fatigue, immune changes, increased heart rate, insomnia, intestinal inflammation, loose stool, menstrual changes, migraine, nausea, stomach pain, and vomiting.

Use cautiously in people with hormone-sensitive cancers such as breast, ovarian, or uterine cancer, or hormone-sensitive conditions such as endometriosis.

Soy may increase the risk of bleeding. Caution is advised in people with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.

Soy may lower blood sugar levels. Caution is advised in people with diabetes or low blood sugar, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood sugar levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.

Soy may cause high blood pressure. Caution is advised in people taking drugs or herbs and supplements that alter blood pressure.

Because soy contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.

Soy may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system.

Use cautiously in people who have anemia, cystic fibrosis, or disorders of the thyroid, stomach, intestine, immune system, or heart.

Avoid with a known allergy to soy, any of its parts, or members of its plant family.

Avoid soy at levels higher than normally consumed in food if the person is pregnant or lactating, has cancer or is at risk for cancer, or is taking medications.

Pregnancy and Breastfeeding

Soy as a part of the regular diet is traditionally considered to be safe during pregnancy and breastfeeding, although scientific research is limited in these areas.

Recent study demonstrates that isoflavones are transferred through breast milk from mothers to infants. In non-human study, high doses of isoflavones resulted in tumors and reproductive changes in offspring. Avoid high doses of soy or soy isoflavones in humans.

This evidence-based monograph was prepared by The Natural Standard Research Collaboration