Isoniazid Side Effects

Medically reviewed by Drugs.com. Last updated on Nov 26, 2024.

Applies to isoniazid: solution, tablet.

Important warnings This medicine can cause some serious health issues

Intramuscular route (solution)

Severe and sometimes fatal hepatitis has been reported with isoniazid therapy and may occur even after many months of treatment.

The risk for hepatitis increases with advancing age, concomitant alcohol use, chronic liver disease, and injection drug use.

Patients given isoniazid should be carefully monitored and interviewed at monthly intervals.

For persons 35 and older, in addition to monthly symptom reviews, hepatic enzymes (specifically, AST and ALT (formerly SGOT and SGPT, respectively) should be measured prior to starting isoniazid therapy and periodically throughout treatment.

An increased risk of fatal hepatitis associated with isoniazid has been reported in women, particularly black and Hispanic women.

The risk may also be increased during the post partum period.

More careful monitoring should be considered in these groups, possibly including more frequent laboratory monitoring.

Oral route (tablet; syrup)

Severe and sometimes fatal hepatitis has been reported with isoniazid therapy and may occur even after many months of treatment.

The risk for hepatitis increases with advancing age, concomitant alcohol use, chronic liver disease, and injection drug use.

Patients given isoniazid should be carefully monitored and interviewed at monthly intervals.

For persons 35 and older, in addition to monthly symptom reviews, hepatic enzymes (specifically, AST and ALT (formerly SGOT and SGPT, respectively) should be measured prior to starting isoniazid therapy and periodically throughout treatment.

An increased risk of fatal hepatitis associated with isoniazid has been reported in women, particularly black and Hispanic women.

The risk may also be increased during the post partum period.

More careful monitoring should be considered in these groups, possibly including more frequent laboratory monitoring.

Serious side effects of isoniazid

Along with its needed effects, isoniazid may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking isoniazid:

More common side effects

• clumsiness or unsteadiness
• dark urine
• loss of appetite
• nausea or vomiting
• numbness, tingling, burning, or pain in hands and feet
• unusual tiredness or weakness
• yellow eyes or skin

Rare side effects

• blurred vision or loss of vision, with or without eye pain
• convulsions (seizures)
• fever and sore throat
• joint pain
• mental depression
• mood or other mental changes
• skin rash
• unusual bleeding or bruising

Other side effects of isoniazid

Some side effects of isoniazid may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common side effects

• diarrhea
• stomach pain

For injection form

• irritation at the place of injection

Dark urine and yellowing of the eyes or skin (signs of liver problems) are more likely to occur in patients over 50 years of age.

For healthcare professionals

Applies to isoniazid: intramuscular solution, oral syrup, oral tablet.

General adverse events

The most commonly reported side effects included mild and transient elevation of serum transaminase levels, peripheral neuropathy, and hepatitis.^[Ref]

Hepatic

• Very common (10% or more): Mild and transient elevation of serum transaminase levels (up to 20%)
• Uncommon (0.1% to 1%): Hepatitis
• Frequency not reported: Abnormal liver function, bilirubinemia, jaundice, mild liver dysfunction, severe hepatitis/fatal hepatitis^[Ref]

Mild and transient elevation in serum transaminases usually occurred in the first 1 to 6 months of treatment, but could occur at any time during treatment. Transaminase levels returned to normal with continued treatment in most cases.^[Ref]

Nervous system

• Common (1% to 10%): Peripheral neuropathy
• Frequency not reported: Convulsions, memory impairment, optic neuritis, paresthesia of the feet/hands, toxic encephalopathy^[Ref]

Peripheral neuropathy usually occurred with doses over 5 mg/kg.^[Ref]

Dermatologic

• Rare (0.01% to 0.1%): Eosinophilia systemic symptoms, toxic epidermal necrolysis
• Frequency not reported: Allergic skin reaction, alopecia, drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome, erythema multiforme, exfoliative dermatitis, exfoliative skin eruptions, maculopapular skin eruptions, morbilliform skin eruptions, purpura, purpuric skin eruptions, rash, skin eruptions^[Ref]

Hematologic

• Frequency not reported: Agranulocytosis, anemia, aplastic anemia, eosinophilia, hemolytic anemia, lymphadenopathy, sideroblastic anemia, thrombocytopenia^[Ref]

Metabolic

• Frequency not reported: Anorexia, hyperglycemia, metabolic acidosis, pellagra, pyridoxine deficiency^[Ref]

Gastrointestinal

• Frequency not reported: Epigastric distress, nausea, pancreatitis, vomiting^[Ref]

Other

• Frequency not reported: Fatigue, fever, malaise, weakness^[Ref]

Psychiatric

• Frequency not reported: Psychosis, toxic psychosis^[Ref]

Musculoskeletal

• Frequency not reported: Lupoid syndrome, systemic lupus erythematosus-like syndrome^[Ref]

Ocular

• Frequency not reported: Optic atrophy^[Ref]

Genitourinary

• Frequency not reported: Bilirubinuria^[Ref]

Cardiovascular

• Frequency not reported: Vasculitis^[Ref]

Endocrine

• Frequency not reported: Gynecomastia^[Ref]

Immunologic

• Frequency not reported: Rheumatic syndrome^[Ref]

Local

• Frequency not reported: Local irritation^[Ref]

Further information

Isoniazid side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer