Background: Most modern studies about human marijuana use have been made under a set of arbitrary cultural standards and policies not related to drug harm potential, loosely called Prohibition. Here we asked if potential health hazards generated by Prohibition are addressed in research design and analysis. Methods: For this, we have searched PubMed database (from inception to December 2017) for citations of prevalent contaminants of illegal street cannabis: fungi and pesticides. In addition, we performed full text evaluation of 23 studies selected from, and including, 2 meta-analysis reviews investigating potential health hazards from cannabis use. Results: Different combinations of the keywords cannabis, prohibition, pesticides, fungi, contaminants, cancer, schizophrenia, psychosis, show that these words coincide in less than 1% of the cannabis human studies within the database. In the scope of 141 abstracts in which the terms, cannabis and pesticides coincide, none is directed to distinguish cannabis and pesticide adverse effects on CNS. A similar picture emerges when fungi is the paired word. Full text evaluation shows that all but one of the studies analyzed, completely neglect or comment on the nature of cannabis source, legal status, or contamination as a confounding factor. Discussion: Our results show a potential bias on scientific investigation that may affect data reliability in informing about the health hazards of cannabis use. This finding suggests that other aspects of the Prohibition environment may also go unacknowledged. Conclusion: Prohibition related health risks usually go unacknowledged and unaccounted for in biomedical research on Cannabis.