Isoniazid may interfere with the activity of other nutrients, including vitamin B3 (niacin), vitamin B12, vitamin D, and vitamin E, folic acid, calcium, and magnesium.^{1 , 2} Supplementation with vitamin B6 is thought to help prevent isoniazid-induced niacin deficiency; however, small amounts of vitamin B6 (e.g. 10 mg per day) appear to be inadequate in some cases.³ People should consider using a daily multivitamin-mineral supplement during isoniazid therapy.

Isoniazid is capable of causing vitamin B3 (niacin) deficiency, most likely due to its ability to interfere with cell-repair enzymes made from niacin. Significant niacin deficiency, also known as pellagra, features dermatitis, diarrhea, and dementia (impaired intellectual function). Supplementation with vitamin B6 is thought to reduce this risk, although small amounts (e.g. 10 mg daily) has been noted to be inadequate in some cases.⁴

Many antibiotics taken by mouth, including isoniazid, may kill friendly bacteria in the large intestine that produce vitamin K.⁵ Vitamin K1 (phylloquinone) is now found in some multivitamins.

Isoniazid may interfere with the activity of other nutrients, including vitamin B3 (niacin), vitamin B12, vitamin D, and vitamin E, folic acid, calcium, and magnesium.^{6 , 7} Supplementation with vitamin B6 is thought to help prevent isoniazid-induced niacin deficiency; however, small amounts of vitamin B6 (e.g. 10 mg per day) appear to be inadequate in some cases.⁸ People should consider using a daily multivitamin-mineral supplement during isoniazid therapy.

Isoniazid may interfere with the activity of other nutrients, including vitamin B3 (niacin), vitamin B12, vitamin D, and vitamin E, folic acid, calcium, and magnesium.^{9 , 10} Supplementation with vitamin B6 is thought to help prevent isoniazid-induced niacin deficiency; however, small amounts of vitamin B6 (e.g. 10 mg per day) appear to be inadequate in some cases.¹¹ People should consider using a daily multivitamin-mineral supplement during isoniazid therapy.

Isoniazid may interfere with the activity of other nutrients, including vitamin B3 (niacin), vitamin B12, vitamin D, and vitamin E, folic acid, calcium, and magnesium.^{12 , 13} Supplementation with vitamin B6 is thought to help prevent isoniazid-induced niacin deficiency; however, small amounts of vitamin B6 (e.g. 10 mg per day) appear to be inadequate in some cases.¹⁴ People should consider using a daily multivitamin-mineral supplement during isoniazid therapy.

Isoniazid may interfere with the activity of other nutrients, including vitamin B3 (niacin), vitamin B12, vitamin D, and vitamin E, folic acid, calcium, and magnesium.^{15 , 16} Supplementation with vitamin B6 is thought to help prevent isoniazid-induced niacin deficiency; however, small amounts of vitamin B6 (e.g. 10 mg per day) appear to be inadequate in some cases.¹⁷ People should consider using a daily multivitamin-mineral supplement during isoniazid therapy.

Isoniazid may interfere with the activity of other nutrients, including vitamin B3 (niacin), vitamin B12, vitamin D, and vitamin E, folic acid, calcium, and magnesium.^{18 , 19} Supplementation with vitamin B6 is thought to help prevent isoniazid-induced niacin deficiency; however, small amounts of vitamin B6 (e.g. 10 mg per day) appear to be inadequate in some cases.²⁰ People should consider using a daily multivitamin-mineral supplement during isoniazid therapy.

Picrorhiza (Picrorhiza kurroa) is an herb from India with well-established anti-inflammatory and liver protective actions.²³ Use of a combination formula known as Liv.100 that contains picrorhiza protected animal livers against damage caused by isoniazid and other antituberculosis antibiotics.²⁴

The potent anti-inflammatory substance known as glycyrrhizin from licorice has been combined with isoniazid for treatment of tuberculosis. An older study found a benefit from combining the two compared to using isoniazid alone.²⁵ Glycyrrhizin was given by injection, so it is not certain if licorice extracts containing glycyrrhizin would be as effective given by mouth. The treatment required at least three months of administration.

Isoniazid has some monoamine oxidase inhibitor (MAOI) activity.²⁶ Isoniazid can alter metabolism of tyramine-containing foods, leading to reactions associated with MAOI drugs (diarrhea, flushing, sweating, pounding chest, dangerous changes in blood pressure, and other symptoms).²⁷ People taking isoniazid should avoid tyramine-containing foods. Isoniazid can also alter metabolism of histamine-containing foods, leading to headaches, sweating, pounding chest, flushing, diarrhea, low blood pressure, and itching.²⁸ People taking isoniazid should avoid histamine-containing foods (such as tuna, sauerkraut juice, or yeast extract).

Isoniazid has some monoamine oxidase inhibitor (MAOI) activity.²⁹ Isoniazid can alter metabolism of tyramine-containing foods, leading to reactions associated with MAOI drugs (diarrhea, flushing, sweating, pounding chest, dangerous changes in blood pressure, and other symptoms).³⁰ People taking isoniazid should avoid tyramine-containing foods. Isoniazid can also alter metabolism of histamine-containing foods, leading to headaches, sweating, pounding chest, flushing, diarrhea, low blood pressure, and itching.³¹ People taking isoniazid should avoid histamine-containing foods (such as tuna, sauerkraut juice, or yeast extract).

Isoniazid can interfere with the activity of vitamin B6.³² Vitamin B6 supplementation is recommended, especially in people with poor nutritional status, to prevent development of isoniazid-induced peripheral neuritis (inflamed nerves).³³ One case is reported in which injectable vitamin B6 reversed isoniazid-induced coma.³⁴ In another case, however, 10 mg per day of vitamin B6 failed to reverse isoniazid-induced psychosis. The author suggested that higher amounts (e.g., 50 mg per day) may be needed.³⁵ Although the optimal amount remains unknown, some doctors suggest that adults taking isoniazid supplement with 100 mg of vitamin B6 per day to prevent side effects. However, as animal studies suggest that very large amounts of vitamin B6 can interfere with the effect of isoniazid,³⁶people taking isoniazid should consult their doctor to determine the appropriate amount of vitamin B6 to take.