Street (or home grown) vs medical cannabis

It's important to understand the differences

Have questions about Medical Cannabis?
Consult our FAQs
Jump to

Quality Control

The foremost difference between street cannabis and medical cannabis is quality control. As the street cannabis market is, by definition, illegal, regulatory bodies do not impose standards or testing requirements. In contrast, medical cannabis in Australia is highly regulated to ensure patient safety and consistency of product formulation.

A number of safety concerns result from the lack of quality control of street cannabis. Without complete chemical analysis in a certified laboratory, the composition of street cannabis is essentially unknown1. It follows that concentrations of the psychoactive element, THC (tetrahydrocannabinol), may be significantly higher than expected, increasing risk of adverse events. In addition, contamination of street cannabis with microbes, pesticides and harmful diluents cannot be ruled out.

Microbial Contamination

Cannabis is host to a number of microorganisms. The majority are harmless and cannot be transmitted to humans, however, there are some exceptions2. Human pathogens can be introduced to the plant from soil, fertiliser, decay during storage or human handling,3. Patients using street cannabis for medical purposes are more likely to be immunocompromised as a result of their disease or its treatment; opportunistic pathogens can pose a threat to these individuals4.

A study of illicit cannabis from coffeeshops in the Netherlands found that all 11 samples obtained had levels of bacteria and/or fungi exceeding the European Pharmacopoeial limit for inhaled preparations. Pathogens present included E. coli and fungi of the Penicillium, Cladosporium and Aspergillus type5. Some of these microbes produce dangerous toxins such as aflatoxins, which are known carcinogens6.

Numerous case studies have described serious pulmonary aspergillosis in immunocompromised patients who smoked herbal cannabis,7,8,9. In the US, herbal cannabis contaminated with S. muenchen caused an outbreak of 85 cases of enteritis10. An outbreak of hepatitis A in the US was linked to cannabis which had been fertilized with human faeces11.

Combustion of plant material through smoking is not sufficient to eliminate fungal spores12 and microbiological toxins13. Furthermore, attempts by some illegal growers to “heat kill” or pasteurize cannabis plant material do not reduce microbial toxins and spores14. To ensure patient safety, cannabis producers must control all sources of microbial contamination throughout the life cycle of the product.

Medical cannabis in Australia must comply with Therapeutic Goods Order No. 93 (TGO 93), the Australian Standard, which specifically limits content of aflatoxins and ochratoxin A15. Furthermore, medical cannabis is subject to TGO 77 which limits the total microbial count and requires absence of Salmonella, E. coli and S. aureus in certain tests16. The Therapeutic Goods Administration also expects medical cannabis producers to determine the risk to their product from microorganisms not specifically mentioned in their guidelines17.


Street cannabis may contain harmful levels of pesticides from the actions of unscrupulous growers or from inadvertent use of contaminated clones (a cutting taken from an existing plant) or soil18. Research has demonstrated that up to 70% of the pesticide content of herbal cannabis is present in the inhaled smoke19.

A study in Brazil found that 15 of 130 cannabis samples seized by São Paulo state police contained paraquat or glyphosate20. In California, 33% of cannabis concentrate samples (n=57) were found to contain pesticides, the most common of which was paclobutrazol21.

TGO 93 mandates testing of medical cannabis to ensure that pesticides are below the levels specified as safe in the European Pharmacopoeia15


In an attempt to maximise profits, suppliers of street cannabis may add diluents such as tobacco, tiny glass beads1, sand22 or, in one case, lead23 to add bulk to their product.

In Germany, 29 individuals were admitted to hospital with symptoms of lead intoxication. Presence of obvious lead particles in herbal cannabis smoked by the patients indicated that lead had been deliberately added to packages rather than originating from contaminated soil23.

TGO 93 prohibits adulteration of medical cannabis with undeclared substances. It also restricts levels of foreign matter and heavy metals15

Unknown Potency

Street cannabis is most often identified by “strain names” which do not reflect the concentration of active constituents to any degree of accuracy. Furthermore, in the absence of regulation, suppliers can change the labelled name of a product at will24.

In cases where THC/CBD concentration is labelled, it is not a reliable measure of content. A study in the US found that 69% of samples were mislabelled, containing at least 10% more or less than the stated amount of active ingredient25.

Studies have observed a trend of increasing THC content in street cannabis, most likely from prevalence of controlled indoor growing environments and years of selective breeding for THC-predominant plants1. Moreover, illicit preparations which further concentrate the content have been found to contain up to 90% THC27,21. More potent cannabis increases the risk of adverse events such as panic reactions, psychosis and orthostatic hypotension with resultant injury26,24.

A fundamental principle of medical cannabis dosing is to “start low and go slow”, i.e. start at a very low dose of THC to maximise symptom relief while minimising unwanted effects. TGO 93 requires quantitative testing of medical cannabis active ingredients and implements strict labelling standards to ensure consistent dosing15.


Please note: this reference material is informational and does not constitute as advice. Furthermore, the information you are being referred to may not comply with the Australian regulatory environment. GreenChoices recommends any information provided should be discussed with a healthcare professional and does not replace their advice.

  1. McLaren J, Swift W, Dillon P, Allsop S. Cannabis potency and contamination: a review of the literature. Addiction 103(7): -291949, 2008.
  2. McPartland JM. Common names for diseases of Cannabis sativa. Plant Dis 75: 226-227, 1991.
  3. McKernan K, Spangler J, Helbert Y, Lynch RC, Devitt-Lee A, Shang L, Orphe W, Warner J, Foss T, Hudalla CJ, Silva M, Smith DR. Metagenomic analysis of medicinal Cannabis samples; pathogenic bacteria, toxigenic fungi, and beneficial microbes grow in culture-based yeast and mold tests. F1000Res 5: 2471, 2016.
  4. McPartland JM. Microbiological contaminants of marijuana. J Int Hemp Assoc 1: 41-44, 1994.
  5. Hazekamp A. An evaluation of the quality of medicinal grade cannabis in the Netherlands. Cannabinoids 1(1): 1-9, 2006.
  6. Ricordy R, Gensabella G, Cacci E, Augusti Tocco G. Impairment of cell cycle progression by aflatoxin B1 in human cell lines. Mutagenesis 17(3): 241-9, 2002.
  7. Sutton S, Lum BL, Torti FM. Possible risk of invasive pulmonary aspergillosis with marijuana use during chemotherapy for small cell lung cancer. Drug Intell Clin Pharm 20(4): 289-91, 1986.
  8. Hamadeh R, Ardehali A, Locksley RM, York MK. Fatal aspergillosis associated with smoking contaminated marijuana, in a marrow transplant recipient. Chest 94(2): 432-3, 1988.
  9. Cescon DW, Page AV, Richardson S, Moore MJ, boerner S, Gold WL. Invasive Pulmonary Aspergillosis Associated With Marijuana Use in a Man With Colorectal Cancer. J Clin Oncol 26(13): 114808, 2008.
  10. Taylor DN, Wachsmuth IK, Shangkuan YH, Schmidt EV, Barrett TJ, Schrader JS, Scherach CS, McGee HB, Feldman RA, Brenner DJ. Salmonellosis associated with marijuana: a multistate outbreak traced by plasmid fingerprinting.. N Engl J Med 306(21): 1249-53, 1982.
  11. Alexander T. Hepatitis outbreak linked to imported pot. Sinsemilla Tips 7(3): 22, 1987.
  12. Kurup,V.P., A. Resnick, S.L. Kagen, S. H. Cohen and J. N. Fink. Allergenic fungi and actinomycetes in smoking materials and their health implications. Mycopathologia 82: 61-64, 1983.
  13. Llewellyn GC, O'Rear CO. Examination of fungal growth and aflatoxin production on marijuana. Mycopathologia 62: 109-112, 1977.
  14. McKernan K, Spangler J, Zhang L, Tadigotla V, Helbert Y, Foss T, Smith D. Cannabis microbiome sequencing reveals several mycotoxic fungi native to dispensary grade Cannabis flowers. F1000Res 4: 1422, 2015.
  15. Therapeutic Goods Order No. 93 (Standard for Medicinal Cannabis) 2017 (Austl.)
  16. Therapeutic Goods Order No. 77 (Microbiological Standards for Medicines) 2008 (Austl.)
  17. Conforming with TGO 93. Accessed 23 May 2018.
  18. Steep Hill. Steep Hill Study Provides Evidence of Substantial Pesticide Contamination in California Cannabis Clones [press release]. 22 Sept 2017.
  19. Sullivan N, Elzinga S, Raber JC. Determination of pesticide residues in cannabis smoke. J Toxicol 2013: 378168, 2013.
  20. Lanaro R, Costa JL, Cazenave SO, Zanolli-Filho LA, Tavares MF, Chasin AA. Determination of herbicides paraquat, glyphosate, and aminomethylphosphonic acid in marijuana samples by capillary electrophoresis. J Forensic Sci 60: S241-7, 2015.
  21. Raber JC, Elzinga S, Kaplan C. Understanding dabs: contamination concerns of cannabis concentrates and cannabinoid transfer during the act of dabbing. J Toxicol Sci 40: 797–803, 2015.
  22. Delourme J, Delattre C, Godard P, Steenhouwer F, Just N. Respiratory consequences of inhalation of adulterated cannabis. Rev Mal Respir 26(5): 552-6, 2009.
  23. Busse F, Omidi L, Timper K, Leichtle A, Windgassen M, Kluge E, Stumvoll M. Lead poisoning due to adulterated marijuana.. N Engl J Med 358(15): -94564, 2008.
  24. Russo EB. Current Therapeutic Cannabis Controversies and Clinical Trial Design Issues. Front Pharmacol 7: 309, 2016.
  25. Bonn-Miller MO, Loflin MJE, Thomas BF, Marcu JP, Hyke T, Vandrey R. Labeling Accuracy of Cannabidiol Extracts Sold Online. JAMA 318(17): 1708-1709, 2017.
  26. Ashton CH. Pharmacology and effects of cannabis: a brief review. Br J Psychiatry 178: 101-6, 2001.
  27. Romano LL, Hazekamp A. Cannabis oil: chemical evaluation of an upcoming cannabis-based medicine. Cannabinoids 1: 43405, 2013.