The revelation comes after analysis of hashish - which is illegal in Spain - being sold on the streets of Madrid, some of which even smelt like poo.
The study, which was published in Forensic Science International, looked at two forms of cannabis resin: one that sold in ingots (blocks) and one that sold in 'acorns' (small oblong pieces of the drug, shaped as such so they can be easily swallowed before coming out the other end).
93 per cent of acorns were contaminated with E-coli bacteria, which usually live in the intestines of humans and animals, and can be expelled in faecal matter. This is compared to 29.4 percent of ingot samples.
Manuel Perez Moreno, co-author of the study, claimed that 40 per cent of the acorns in the sample actually smelt like human faeces.
Hashish seized by Ansbach criminal police. Credit: PA
In total, 90 samples of cannabis resin were collected by the team, who gathered samples from across the community of Madrid.
They found that 88.3 per cent of the samples were not suitable for consumption.
What's even worse is that Moreno also said the contaminated hashish posed a particular risk for cancer patients who consume it to reduce the side effects of chemotherapy.
He said: "These patients have a weakened immune system, so an infection caused by the consumption of contaminated or adulterated hashish could be fatal."
Most strains of the bacteria are harmless, or may only cause diarrhoea.
However, other strains can cause severe abdominal cramps, vomiting and bloody stool, with the most virulent strains leading to gastroenteritis, urinary tract infections, neonatal meningitis, hemorrhagic colitis and Crohn's disease.
Moreno told Spanish newspaper El Pais that the bacteria is believed to have got into the cannabis resin through the way it is transported, with acorns often wrapped in cling film and ingested before being expelled from the body using laxatives.
Long story short? Sounds like you're probably just best off staying away from the hashish, kids.
Featured Image Credit: PA