Does gabapentin interact with soy products or soy isoflavone supplements, or contain soy-derived ingredients that could affect someone with a soy allergy? | Based on FDA

Short answer

Based on official prescribing information and available pharmacology data, gabapentin does not have known interactions with soy foods or soy isoflavone supplements, and most commonly marketed gabapentin capsule formulations do not list soy-derived excipients. Labels do warn about rare serious allergic reactions to gabapentin itself, but not specifically due to soy ingredients. ^{[1] [2]}

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Does gabapentin interact with soy or soy isoflavones?

• No clinically recognized interaction. Gabapentin has very few drug–drug interactions because it is not metabolized by liver enzymes such as cytochrome P450, is minimally protein-bound, and is eliminated unchanged in urine. This profile makes food, herbal, and supplement interactions uncommon, and there is no documented interaction with soy or soy isoflavones in official labeling or pharmacology reviews. ^{[3] [4]}

• Known interactions are different. The main interaction consistently noted in labeling is with aluminum/magnesium-containing antacids (e.g., Maalox), which can reduce gabapentin’s bioavailability by about 20% if taken at the same time; spacing doses by at least 2 hours is typically advised. This interaction does not involve soy. ^{[1] [5]}

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Do gabapentin products contain soy-derived ingredients?

• Most capsule labels list no soy excipients. Multiple FDA-approved gabapentin capsule medication guides list inactive ingredients such as lactose (anhydrous or monohydrate), corn starch, mannitol, pregelatinized starch, talc, gelatin capsule shells, sodium lauryl sulfate, titanium dioxide, and iron oxide colorants. None of these are soy-derived. ^{[6] [7] [8] [9] [10] [11] [12]}

• Formulations vary by manufacturer and strength. Some labels enumerate different colorants or excipient mixes (e.g., croscarmellose sodium, magnesium stearate), but still do not list soybean oil or soy lecithin. If you have a severe soy allergy, checking the specific National Drug Code (NDC) and manufacturer’s detailed excipient list is prudent, but typical U.S. capsule formulations do not include soy ingredients. ^{[13] [14]}

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Allergy considerations

• Gabapentin can rarely cause serious hypersensitivity reactions. Labels warn about Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), anaphylaxis, and angioedema, which are immune reactions to the drug itself and can occur independently of food allergies. Seek urgent care for swelling of the face or throat, difficulty breathing, rash with fever, or other systemic symptoms after starting gabapentin. ^{[2] [15] [16]}

• Not a soy-specific warning. These allergy warnings are not linked to soy-derived excipients on standard capsule labels, and there is no cross-reactivity noted between soy allergy and gabapentin. ^{[2] [17]}

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Practical guidance for people with soy allergy

• Review your exact product’s label. While U.S. gabapentin capsules commonly lack soy excipients, confirm the inactive ingredients on your specific product’s medication guide or pharmacy label, especially if you use a non-capsule formulation or an international product. ^{[9] [10]}

• Ask the pharmacist. Pharmacists can verify the excipient list tied to your product’s NDC and help source a soy-free manufacturer if you have a history of severe soy reactions. This is a practical step because excipients can vary across suppliers. ^{[10] [11]}

• Monitor for allergic symptoms. If you develop hives, swelling, or breathing issues, stop the medication and seek care immediately, as this may reflect a gabapentin hypersensitivity reaction rather than a soy exposure. ^{[2] [16]}

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Key points to remember

• No known interaction with soy foods or soy isoflavones. Gabapentin’s pharmacokinetics and official labeling do not indicate a concern with soy products. ^{[3] [4]}

• Most capsule formulations do not list soy-derived excipients. Common inactive ingredients are lactose, starches, talc, gelatin, and colorants, not soy. ^{[6] [7]}

• Main interaction to consider is antacids with aluminum/magnesium. Separate dosing to avoid reduced absorption. ^{[1] [18]}

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Ingredient reference table (examples from U.S. capsule labels)

Manufacturer/Label Example	Active Ingredient	Common Inactive Ingredients (Examples)	Soy-Derived Ingredient Listed?
Gabapentin Capsules (various labels)	Gabapentin	Corn starch, lactose monohydrate, talc; capsule shell with gelatin, sodium lauryl sulfate, titanium dioxide; iron oxides for color	No [6] [7]
Gabapentin Capsules, USP	Gabapentin	Magnesium stearate, pregelatinized starch, starch, talc; capsule shell with gelatin, sodium lauryl sulfate, titanium dioxide, iron oxides	No [8] [9]
Alternate capsule labels	Gabapentin	Mannitol, pregelatinized starch, talc; colorants FD&C Red 40, D&C Yellow 10, titanium dioxide	No [11] [12]
Granules Pharmaceuticals capsule	Gabapentin	Croscarmellose sodium, magnesium stearate; capsule processing agents (iron oxides, alcohols); purified water	No soy named [13] [14]

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Bottom line

Evidence suggests gabapentin does not interact with soy foods or soy isoflavone supplements, and standard U.S. capsule formulations do not include soy-derived excipients; however, because excipients can vary by manufacturer, people with severe soy allergy should verify the specific product’s inactive ingredients and consult their pharmacist. ^{[3] [6] [10] [2]}