Benznidazole Side Effects

Medically reviewed by Drugs.com. Last updated on Apr 14, 2025.

Applies to benznidazole: oral tablet.

Serious side effects of benznidazole

Along with its needed effects, benznidazole 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 benznidazole:

More common side effects

• black, tarry stools
• chest pain
• chills
• cough
• fever
• painful or difficult urination
• rash
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• swollen glands
• unusual bleeding or bruising
• unusual tiredness or weakness

Less common side effects

• burning, numbness, tingling, or painful sensations
• headache
• tremors
• unsteadiness or awkwardness
• weakness in the arms, hands, legs, or feet

Incidence not known

• bleeding gums
• blistering, peeling, or loosening of the skin
• blood in the urine or stools
• dark urine
• diarrhea
• difficulty in moving
• general tiredness and weakness
• inability to concentrate
• itching
• light-colored stools
• muscle pain or stiffness
• nausea
• pain, swelling, or redness in the joints
• pinpoint red spots on the skin
• red, irritated eyes
• seizures
• swelling of the eyelid, arms, or legs
• swollen, painful, or tender lymph glands in the neck, armpit, or groin
• temporary disorientation
• temporary loss of memory
• trouble sleeping
• upper right abdominal pain
• vomiting
• yellow eyes and skin

Other side effects of benznidazole

Some side effects of benznidazole 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

• decreased appetite
• decreased weight
• stomach pain

Incidence not known

• bone pain
• dry mouth
• loss of sense of taste
• loss of strength
• muscle aching or cramping

For healthcare professionals

Applies to benznidazole: oral tablet.

General adverse events

This drug was used in 55 pediatric patients (aged 6 to 12 years) and 64 pediatric patients (aged 7 to 12 years) during 2 controlled trials and 37 pediatric patients (aged 2 to 12 years) in an uncontrolled trial; each patient had chronic indeterminate Chagas disease.

In 1 controlled trial, this drug was discontinued due to at least 1 side effect in 5 of 55 patients; such side effects included abdominal pain, nausea, vomiting, rash, decreased appetite, headache, and elevated transaminases. The most commonly reported side effects in this trial were abdominal pain, rash, decreased weight, and headache.

In the uncontrolled trial, rash, leukopenia, urticaria, eosinophilia, decreased appetite, and neutropenia were reported in 6 of 19 pediatric patients (aged 2 to 6 years); such side effects were similar to those reported in the overall population of 37 patients.^[Ref]

Gastrointestinal

• Very common (10% or more): Abdominal pain (up to 25%)
• Common (1% to 10%): Nausea, vomiting, diarrhea
• Postmarketing reports: Epigastric pain, dry mouth^[Ref]

Dermatologic

• Very common (10% or more): Rash (16%), urticaria (16%), skin lesions (11%)
• Frequency not reported: Severe skin and soft tissue reactions, serious skin and subcutaneous disorders, extensive skin reactions (such as rash [maculopapular, pruritic macules, eczema, pustules, allergic dermatitis])
• Postmarketing reports: Maculopapular cutaneous eruptions, erythematous plaques, generalized rash, erythematous rash, pruritic rash, blistering eruptions, peeling skin, exfoliative dermatitis, toxic epidermal necrolysis, acute generalized exanthematous pustulosis, erythema multiforme, drug reaction with eosinophilia and systemic symptoms (DRESS)^[Ref]

Extensive skin reactions (such as rash [maculopapular, pruritic macules, eczema, pustules, erythematous, generalized, allergic dermatitis, exfoliative dermatitis]) have been reported. Most cases occurred after about 10 days of therapy; most rashes resolved with discontinuation of therapy.^[Ref]

Hematologic

• Very common (10% or more): Leukopenia (16%), eosinophilia (16%), neutropenia (16%)
• Frequency not reported: Hematological manifestations of bone marrow depression (such as neutropenia, thrombocytopenia, anemia, leukopenia)
• Postmarketing reports: Lymphadenopathy, thrombocytopenia, granulocytopenia, agranulocytosis^[Ref]

Metabolic

• Very common (10% or more): Decreased appetite (up to 16%)
• Common (1% to 10%): Anorexia^[Ref]

Other

• Very common (10% or more): Decreased weight (13%)
• Frequency not reported: Genotoxicity
• Postmarketing reports: Fever, asthenia, fatigue, generalized edema, edema in the extremities, elevated alkaline phosphatase^[Ref]

Nervous system

• Common (1% to 10%): Headache, dizziness, peripheral neuropathy, tremor
• Postmarketing reports: Paresthesia, hypoesthesia, headaches, convulsions, inability to concentrate, temporary amnesia, ageusia^[Ref]

Hepatic

• Common (1% to 10%): Elevated transaminases
• Postmarketing reports: Hepatitis, toxic hepatitis, elevated bilirubin

Another nitroimidazole agent structurally related to this drug:

• Postmarketing reports: Severe irreversible hepatotoxicity/acute liver failure in patients with Cockayne syndrome^[Ref]

Cases of severe irreversible hepatotoxicity/acute liver failure, including cases with fatal outcomes with very rapid onset after start of systemic use of metronidazole (another nitroimidazole agent structurally related to this drug), have been reported in patients with Cockayne syndrome; latency from drug start to signs of liver failure has been as short as 2 days.^[Ref]

Musculoskeletal

• Common (1% to 10%): Arthralgia
• Postmarketing reports: Myalgia, musculoskeletal pain, migratory arthritis^[Ref]

Psychiatric

• Postmarketing reports: Insomnia, temporary disorientation^[Ref]

Ocular

• Postmarketing reports: Eyelid edema^[Ref]

Further information

Benznidazole 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