Mebendazole or Fenbendazole

Our assessments of evidence for each medical benefit fall into one of these categories:

• Strong evidence: consistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results
• Good evidence: significant effects in one large or several mid-sized and well-designed clinical studies ( randomized controlled trialsa study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects with an appropriate placebo or other strong comparison control or observational studies that control for confounds)
• Modest evidence: significant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies), or several small studies aggregated into a meta-analysis
• Preliminary evidence: significant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect
• Weak evidence: one or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects
• Insufficient evidence: preclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example)

Learn more about how we research and rate therapies and practices in How We Rate Therapies ›

Advanced colorectal cancer

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of better tumor responses including slower disease progression after treatment with chemotherapy among people with metastatic colorectal cancer treated with mebendazole

• Better tumor response rate, longer progression-free survivalthe time during and after treatment of a disease that a patient lives without disease progression (worsening), and a weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently towards lower serum concentrations of carcinoembryonic antigen (CEA) after treatment with bevacizumab and FOLFOX4 among people with metastatic colorectal cancer treated with 500 mg oral mebendazole twice a day for 12 weeks compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹Hegazy SK, El-Azab GA, Zakaria F, Mostafa MF, El-Ghoneimy RA. Mebendazole; from an anti-parasitic drug to a promising candidate for drug repurposing in colorectal cancer. Life Sciences. 2022 Jun 15;299:120536.
• After disease progression and metastasis following treatment with capecitabine, oxaliplatin, and bevacizumab followed by capecitabine and irinotecan, a man with metastatic colon cancer achieved partial remission after treatment with 100 mg mebendazole twice a day for 6 weeks, decreased after showing elevated liver enzymes in a case studya descriptive and exploratory analysis of a person, group, or event regarding changes observed over time; because changes due to treatment are not compared to similar changes over time without treatment, a case study is considered a weak study design²Nygren P, Larsson R. Drug repositioning from bench to bedside: tumour remission by the antihelmintic drug mebendazole in refractory metastatic colon cancer. Acta Oncologica. 2014 Mar;53(3):427-8.

Preliminary evidence of lower levels of vascular endothelial growth factora substance made by cells, including cancer cells, that stimulates new blood vessel formation (VEGF)—which promotes development of the blood supply for tumors—after treatment with bevacizumab with FOLFOX4 among people with metastatic colorectal cancer also treated with mebendazole

• Lower levels of VEGF after treatment with bevacizumab with FOLFOX4 among people with metastatic colorectal cancer also treated with 500 mg oral mebendazole twice a day for 12 weeks compared to placebo in a small RCT³Hegazy SK, El-Azab GA, Zakaria F, Mostafa MF, El-Ghoneimy RA. Mebendazole; from an anti-parasitic drug to a promising candidate for drug repurposing in colorectal cancer. Life Sciences. 2022 Jun 15;299:120536.

Advanced endocrine cancer: weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of stable disease for 19 months, then progression 24 months after beginning treatment with mebendazole in a man with metastatic adrenocortical carcinoma

• After disease progression following systemic therapies including mitotane, 5-fluorouracil, streptozotocin, bevacizumab, and external beam radiation therapy, a man with metastatic adrenocortical carcinoma achieved stable disease for 19 months, then progression 24 months after beginning monotherapy of 100 mg mebendazole twice a day in a case study⁴Dobrosotskaya IY, Hammer GD, Schteingart DE, Maturen KE, Worden FP. Mebendazole monotherapy and long-term disease control in metastatic adrenocortical carcinoma. Endocrine Practice. 2011 May-Jun;17(3):e59-62.

Also see evidence of accelerated disease progression among people with refractory gastrointestinal cancer treated with mebendazole in Safety and precautions ›

No evidenceoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. of a meaningful effect among people with recurrent glioblastoma not eligible for re-radiation treated with mebendazole plus either lomustine or temozolomide

• No evidence of an effect (failure to achieve 55% survival at 9 months) among people with recurrent glioblastoma not eligible for re-radiation treated with mebendazole plus either lomustine or temozolomide compared to baseline in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects⁵Patil VM, Menon N et al. Mebendazole plus lomustine or temozolomide in patients with recurrent glioblastoma: a randomised open-label phase II trial. EClinicalMedicine. 2022 May 27;49:101449.

Mebendazole and temozolomide: weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of longer progression-free survivalthe time during and after treatment of a disease that a patient lives without disease progression (worsening) after completing concurrent radiation plus temozolomide among people with newly diagnosed high-grade gliomas treated with temozolomide and mebendazole

• A trend toward longer progression-free survival after completing concurrent radiation plus temozolomide among people with newly diagnosed high-grade gliomas treated with temozolomide and mebendazole for more than 1 month compared to less than 1 month in a small uncontrolled triala study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design⁶Gallia GL, Holdhoff M et al. Mebendazole and temozolomide in patients with newly diagnosed high-grade gliomas: results of a phase 1 clinical trial. Neuro-oncology Advances. 2020 Nov 12;3(1):vdaa154.

Simvastatin, metformin, niclosamide, mebendazole, itraconazole, loratadine, and chloroquine: weak evidence of improved symptoms, progression-free survival, and overall survival for a few months after failing to respond to 2 courses of chemotherapy in a woman with recurrent platinum-resistant clear-cell ovarian cancer treated with simvastatin, metformin, niclosamide, mebendazole, itraconazole, loratadine, and chloroquine

• Improved symptoms for 4 months, progression-free survival for 2 months, and overall survival for 8.5 months after failing to respond to 2 courses of chemotherapy in a woman with recurrent platinum-resistant clear-cell ovarian cancer treated with simvastatin, metformin, niclosamide, mebendazole, itraconazole, loratadine, and chloroquine in a case studya descriptive and exploratory analysis of a person, group, or event regarding changes observed over time; because changes due to treatment are not compared to similar changes over time without treatment, a case study is considered a weak study design⁷Sinsuwan W, Norchai P. Repurposing drugs in controlling recurrent platinum-resistant clear-cell ovarian cancer. Case Reports in Oncologoical Medicine. 2023 Jun 7;2023:2079654.

Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of higher percentages of probiotic and anti-inflammatory microbes among children treated with mebendazole for parasites (not specific to cancer)

• Higher percentages of the known probiotic species Streptococcus thermophilus and another anti-inflammatory bacterium, Collinsella aerofaciens, among primary school children in Taiwan treated with 100 mg mebendazole for deworming compared to no mebendazole in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁸Yang CA, Liang C et al. Impact of Enterobius vermicularis infection and mebendazole treatment on intestinal microbiota and host immune response. PLoS Neglected Tropical Diseases. 2017 Sep 25;11(9):e0005963.