The full article

What is Metronidazole? 

Metronidazole is an antibiotic that belongs to the nitroimidazole class of antibiotics. 

It is used to treat bacterial infections in the gastrointestinal tract and parasitic infections such as giardiasis, amoebiasis, and trichomoniasis in humans(1).  However, veterinarians also use metronidazole for dogs experiencing inflammatory bowel disease.

With added antiparasitic properties, metronidazole sits apart from any other antibacterial meds, allowing it to treat a wide variety of infections. It is available in the following dosage form: tablet, capsule, and powder for suspension(2)

The extended-release (meaning it is formulated so that the tablet is slowly released in the body) is used to treat women with vaginal infections (bacterial vaginosis). Though it is widely used for treatment, it should be noted that this drug does not work for colds, sore throat, cough, or other virus infections(3)

The most common metronidazole brand in the market is Flagyl, especially the tablet form(4)

How does it work? 

The exact mechanism of action of metronidazole is not fully established. After taking metronidazole, it diffuses into the cells of the target organism, stopping the protein synthesis. 

The nitro group found in the metronidazole interacts with the susceptible microorganism’s DNA. This results in the disruption of the helical structure and strand breakage. Therefore, causing cell death(5)

Can CBD be taken with Metronidazole?

The CBD-drug interaction is mainly characterized by its effect on the cytochrome P450 system (CYP450), which is found in the liver. These key enzymes are responsible for the breakdown of drugs consumed. 

Cannabidiol, on the other hand, acts as a competitive inhibitor of CYP450. This means that CBD draws the attention of these enzymes largely from metabolizing other drugs or compounds(6)

Furthermore, CBD halts the CPY450 action on other substances it would normally metabolise. And this leads to an overall increase in processing time. 

On the other hand, antibiotics also utilizes the CYP450 enzyme system. Thus, any antibiotics could interact with CBD since both are using this pathway. 

When the CPY450 system is affected this way, it could cause unwanted side effects and sometimes overdosage. This is because certain drugs are retained in the system at a higher level(7).

The inhibiting effect of the CBD on the liver function might depend on the amount and form used. However, this is not yet well established. 

Can CBD replace Metronidazole? 

CBD has been under investigation for years if it has antimicrobial property. One study investigated how cannabinoids affect pathogenic bacteria. 

In the said study, each cannabinoid was tested against six strains of the antibiotic-resistant bacteria, the methicillin-resistant Staphylococcus aureus (MRSA). All cannabinoids showed potent activity against a variety of MRSA strains(8)

The result of this study proved that CBD has a potent property in inhibiting the growth of MRSA. A promising result to fight off superbugs in the field of medicine. 

Over the years, numerous studies have been conducted to know more about the antibiotic property of CBD. However, there is no known research that suggests CBD as a good replacement for any antibiotics, and as a special interest in this topic, on metronidazole. 


The researches show positive results on CBD’s antimicrobial properties. However, there are no known studies that suggest taking antibiotics and CBDs together, nor recommendations that CBD could replace antibiotics medication for the prevention and treatment of antibiotics and antiparasitic meds. 

There is still a need to conduct more research to establish the effectiveness of CBD as an antibiotic and antiparasitic. 

Until studies that specifically look at how CBD interacts with antibiotics are completed, consult with a doctor to make sure there are no CBD drug interactions with other medications currently taken.

  1. Weir CB, Le JK. Metronidazole. [Updated 2019 Dec 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Retrieved from:
  2. Mayo Clinic. (01 April, 2020) Metronidazole (Oral Route). Retrieved from:
  3. Drug Bank. (June 13, 2005). Metronidazole. Retrieved from:
  4. ibid.
  5. Weir et. al. op. Cit.
  6. Pharmotech SA. CBD Drug Interactions. Retrieved from
  7. ibid.
  8. Giovanni Appendino, G et al. Antibacterial Cannabinoids from Cannabis sativa: A Structure−Activity Study. Journal of Natural Products 2008 71 (8), 1427-1430. DOI: 10.1021/np8002673.

More Info

Less Info


(Group 2B)


For definition of Groups, see Preamble Evaluation.


Supplement 7: (1987) (p. 250)


CAS No.: 443-48-1

Chem. Abstr. Name: 2-Methyl-5-nitro-1H-imidazole-1-ethanol


  1. Evidence for carcinogenicity to humans (inadequate)


Two epidemiological studies [ref: 1,2] of women treated with metronidazole showed some excesses of cancers of the uterine cervix, a neoplasm that has risk factors in common with vaginal trichomoniasis, the main indication in women for treatment with this drug. In one study [ref: 1], a greater excess of cervical cancer was observed in women with trichomoniasis who were not exposed to metronidazole than in those who were (relative risk, 2.1 versus 1.7). An excess of lung cancer (4 observed, 0.6 expected) seen in one of these studies [ref: 1] was not found in the other (2 observed, 2.6 expected) [ref: 3]. In the former, the excess was mainly of adenocarcinoma (3/4 cases) and was concentrated after at least ten years from first use of metronidazole (3 observed, 0.3 expected) [ref: 4]. Further follow-up and analysis of these data have suggested that the excess could be explained entirely by confounding with smoking [ref: 5]. Another study in which 12 280 users of metronidazole were followed up for two and one-half years gave a relative risk of 0.89 (95% confidence interval, 0.45-1.9) for all cancers [ref: 6].


  1. Evidence for carcinogenicity to animals (sufficient)


Metronidazole has been tested for carcinogenicity by oral administration in mice and rats. It significantly increased the incidences of lung tumours in mice of each sex, of lymphomas in female mice [ref: 7,8] and of mammary, pituitary, testicular and liver tumours in rats [ref: 7,9,10]. It increased the incidence of colonic tumours induced in rats by subcutaneous administration of 1,2-dimethylhydrazine [ref: 11,12].


  1. Other relevant data


Studies on bone-marrow cells and lymphocytes from a series of patients treated with metronidazole showed no increase in the incidence of chromosomal damage. Metronidazole was active in body fluid assays using sweat, faeces and urine from humans exposed in vivo and urine from rodents exposed in vivo [ref: 13].


Metronidazole did not induce micronuclei in bone-marrow cells of mice or rats, sister chromatid exchanges in bone-marrow cells of Chinese hamsters or unscheduled DNA synthesis in germ cells of male rabbits treated in vivo. Human cells exposed to metronidazole in vitro did not show increased incidences of chromosomal aberrations, whereas results with respect to sister chromatid exchanges were inconclusive. Metronidazole did not induce sister chromatid exchanges in cultured hamster cells; conflicting results were reported for the induction of mutation and DNA damage in rodent cells in vitro. It did not induce sex-linked recessive lethal mutations in Drosophila or recombination in yeast. It induced mutation in fungi and bacteria and induced prophage in bacteria [ref: 13].


Overall evaluation


Metronidazole is possibly carcinogenic to humans (Group 2B).


For definition of the italicized terms, see Preamble Evaluation.


Also see previous evaluation: Vol. 13 (1977)




  1. Beard, C.M., Noller, K.L., O’Fallon, W.M., Kurland, L.T. & Dockerty, M.B. (1979) Lack of evidence for cancer due to use of metronidazole. New Engl. J. Med., 301, 519-522


  1. Friedman, G.D. & Ury, H.K. (1980) Initial screening for carcinogenicity of commonly used drugs. J. natl Cancer Inst., 65, 723-733


  1. Friedman, G.D. (1980) Cancer after metronidazole. New Engl. J. Med., 302, 519


  1. Beard, C.M. (1980) Cancer after metronidazole. New Engl. J. Med., 302, 520


  1. Beard, C., Noller, K. & O’Fallon, W.M. (1985) Metronidazole and subsequent malignant neoplasms (Abstract). Am. J. Epidemiol., 122, 529


  1. Danielson, D.A., Hannan, M.T. & Jick, H. (1982) Metronidazole and cancer. J. Am. med. Assoc., 247, 2498-2499


  1. IARC Monographs, 13, 113-122, 1977


  1. Cavaliere, A., Bacci, M., Amorosi, A., Del Gaudio, M. & Vitali, R. (1983) Induction of lung tumors and lymphomas in BALB/c mice by metronidazole. Tumori, 69, 379-382


  1. Rustia, M. & Shubik, P. (1979) Experimental induction of hepatomas, mammary tumors, and other tumors with metronidazole in noninbred Sas:MRC(WI)BR rats. J. natl Cancer Inst., 63, 863-868


  1. Cavaliere, A., Bacci, M. & Vitali, R. (1984) Induction of mammary tumors with metronidazole in female Sprague-Dawley rats. Tumori, 70, 307-311


  1. Sloan, D.A., Fleiszer, D.M., Richards, G.K., Murray, D. & Brown, R.A. (1983) Increased incidence of experimental colon cancer associated with long-term metronidazole therapy. Am. J. Surg., 145, 66-70


  1. A-Kareem, A.M., Fleiszer, D.M., Richards, G.K., Senterman, M.K. & Brown, R.A. (1984) Effect of long-term metronidazole (MTZ) therapy on experimental colon cancer in rats. J. surg. Res., 36, 547-552


  1. IARC Monographs, Suppl. 6, 399-402, 1987







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Last updated: 3 March 1998


See Also:

        Metronidazole (IARC Summary & Evaluation, Volume 13, 1977)

        Metronidazole (PIM 347)




VOL.: 13 (1977) (p. 113)


  1. Summary of Data Reported and Evaluation

5.1 Animal data

Metronidazole is carcinogenic in mice after its oral administration: it significantly increased the incidence of lung tumours in both sexes and the incidence of lymphomas in females. Its oral administration to rats increased the incidence and multiplicity of mammary fibroadenomas.


5.2 Human data

No case reports or epidemiological studies were available to the Working Group.


Subsequent evaluation: Suppl. 7 (1987)


Last updated: 25 March 1998


See Also:

        Metronidazole (IARC Summary & Evaluation, Supplement 7, 1987)

        Metronidazole (PIM 347)


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