There’s nothing wrong with being confused when it comes to mebendazole and fenbendazole. These two drugs may sound similar when it comes to their names and drug classes, but in fact are very different. Mebendazole is approved for human use while fenbendazole has been developed solely for animal use. This difference in approvals introduces the potential for major differences in safety, dosing, and regulation.

In the last several years, online forums, blog posts, and anecdotal reports have contributed to a perception that the safety and efficacy of mebendazole and fenbendazole is equal, resulting in the ability to prioritize safety over a perceived or real null risk. This is in fact a very dangerous trend, and underscores the importance in understanding the difference in the drugs and the potential consequences of misusing them.

Mebendazole vs. Fenbendazole: One is FDA approved for people. One for animals.

The mebendazole and fenbendazole names are often grouped due to them both being in the class of medications called benzimidazoles. All classes of benzimidazole drugs have the same mechanism of action. Benimidozole drugs disrupt microtubules, which are the basic building blocks for a large number of cellular structures including the parasites that the drugs are designed to kill.

Fenbendazole is a veterinary medicine designed for the deworming of animals ranging from dogs to horses and is not approved for a sale to or use in humans. A number of sections of the regulation and guidelines that govern animal drugs including: strength, purity, safety, and efficacy differ from the corresponding sections for human drugs.

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Due to Mebendazole’s decades of FDA approval and use for treatment of parasitic infections, healthcare professionals can prescribe the medication with certainty. Mebendazole, which treats infections due to hookworms and other parasitic infections, has been used for decades for treatment of parasitic infections. Given the established human dosing guidelines and safety data, mebendazole has been used to treat infections due to hookworms among other parasitic infections.

This distinction holds significance. While animal products that are sold online seem to have similar ingredients to the human medications, they can not be used as substitutes to the human medicines that are regulated.

Fenbendazole and the Story That Raised Questions

Fenbendazole interest sparked due to the running of a 2016 personal account who, while participating in a clinical trial for small-cell lung cancer, fenbendazole independently. Mebendazole was the only participant who had a reaction among the 1,000 trial subjects.

This account even isn’t sufficient to meet the definition of anecdote where case studies are required since they don’t state a cause, safety, nor effectiveness. Even though personal accounts are not adequate, the account must have been in a story form in order to omit a clinical trial.

Anticancer Research stated the following:

“Experimental studies showed insufficient therapeutic performance due to the poor water solubility of fenbendazole, even though it has some positive effects on cancer.”

The first studies on fenbendazole in humans have not been done, despite some studies that showed reduced tumor growth of fenbendazole in animal models and cell cultures, particularly mice. Fenbendazole should not be used in humans due to the absence of human studies, the human absorption, and toxicity (or safety) data, as well as empirical data on dosage.

Mebendazole: How It Works and Why Researchers Are Interested

Mebendazole prevents the synthesis of some microtubules so that the parasites do not have structures (cytoskeleton) to encapsulate themselves and cannot absorb glucose. When glucose is not taken in, the parasites do not have a means to produce energy (via glycolysis) and die so that the body can eliminate them.

Mebendazole is used for parasitic infections, but in scientific studies, has been used because the mechanism of action, in some respects, is similar to that involved in the growth of cancer cells.

What the current research suggests

Cell cycle disruption: Reviews show mebendazole interferes with tubulin polymerization which is a target for some anticancer drugs.
Angiogenesis inhibition: Laboratory studies suggest it may reduce new blood vessel formation in tumor models.
Triple-negative breast cancer: Preclinical research found reduced tumor growth and metastasis in cell and mouse models.
Advanced gastrointestinal cancers: A small exploratory human study using individualized high doses found mebendazole to be generally well tolerated.
Metastatic colorectal cancer: A randomized, placebo-controlled trial showed addition of mebendazole to standard therapy improved response markers and led to longer progression-free intervals.

These observations do not mean mebendazole is an effective anti-cancer drug, however, this is why research continues to study mebendazole under controlled conditions.

Who May Prescribes Mebendazole

Mebendazole is a controlled human drug, therefore, it is only prescribed by accredited clinicians, including:

Infectious disease specialists, especially regarding complicated parasitic infections
Internal medicine physicians who treat adult patients
Family medicine physicians, who often treat infections at the family or household level
Pediatricians, as children are often affected by parasitic infections
Nurse practitioners and physician assistants, within their respective practice limits
Oncologists, mainly for academic discussion and research, not for routine cancer care

Any prescription outside the approved indications is considered off-label, which must be done within strict medical supervision.

Who May Need Mebendazole

Healthcare providers may prescribe mebendazole when there is a confirmed or highly suspected parasitic infection.

Children who itch or move around at night, often due to having pinworms
People in the same household are at risk of getting infected, depending on the level of exposure.
Patients with confirmed intestinal parasites, according to stool testing or symptoms
People inquiring about Research use, where clinicians describe to the patient what the evidence does (or does not) support

The cases are evaluated one by one to ensure the safety and proper dosing.

The Bottom Line

Despite the fact that mebendazole and fenbendazole belong to the same pharmaceutical class and their names are similar, they are not interchangeable. One of these is a lawfully marketed and FDA-approved drug for humans, and the other is a drug that is only for veterinary use. Anecdotal evidence and preliminary research may be interesting, but they cannot replace the need for clinical evidence and proven safety.

The better these differences are understood, the more they help avoid careless choices, as well as stress the reliance on competent health care rather than fraudulent internet fads. For example, especially with new research on the drugs discussed, it is as important to look at the use of the drug as it is to look at where and how it has been approved.