Can drug-sniffing dogs smell the difference between hemp and cannabis?

Published May 20, 2020 12:00 p.m. ET
iStock / ChiccoDodiFC

How well trained is Rover? Police dogs or K9, as we commonly refer to them, are trained to detect illicit drugs accurately. Cannabis and legal hemp are just two of the many drugs that Rover and other K9 officers are trained to detect and react to. However, Rover could soon find himself out of a job. Drug sniffing dogs who work in Ohio may find themselves out of work due to the change in state laws. Ohio's new hemp-legalization law has put some K9 officer's jobs in jeopardy.

Can an old dog be taught new tricks?

A drug-sniffing dogs' ability to detect a drug while aiding in a search enables the human officer to have probable cause to search a person or the possessions of an individual. If Rover, the K9 officer, cannot tell the difference between hemp and marijuana plant, then his job is not secure.

Police dogs are trained to detect several drugs, and marijuana and hemp are two of the many detectable drugs that the police dogs are qualified to seek. However, there is an issue with detecting if the odour is from hemp or a marijuana plant, as the drug-sniffing dogs have trouble doing this. The marijuana plant and the hemp plant smell the same to a dog, so they cannot tell the difference.  Both substances come from the cannabis plant gene pool, which is why they smell similar.

The K9 unit is in jeopardy, specifically the dogs trained for cannabis detection, as it appears that they need to learn some new tricks. Police dogs are trained to sniff and detect specific drugs. Once the dog has been prepared for a specific narcotic, the animal cannot stop reacting to the trained odour. Once a K9 officer is trained for detecting marijuana, it becomes embedded within them, so it’s almost impossible for the K9 officer to learn a new trick.

This causes an issue for the human officer. Is his canine partner signalling the discovery of hemp, marijuana, or cocaine? All police dogs react in the same manner when detecting narcotics. Concerns arise with the legality of the hemp plant being identified as cannabis from the drug-sniffing dogs by mistake.

Nose witness

The K9 officer is responsible for providing a reliable reaction once they have identified an illegal drug. This method and information are then used to assist an officer in moving forward with a search.  Criminal defence lawyers argue that the human officer has no idea what drug the K9 officer is hitting on, as there is evidence that proves the dog will react the same way for hemp, and it would with cannabis.


Different training substances

Ohio Highway Patrol, along with the Columbus Division of Police, has suspended marijuana detection training for their K9 officers. This practice is implemented in the hopes that it will uncomplicate the probable cause issues than are tying up the courts today. No longer will the K9 officers in Ohio be trained for the detection of THC.


The Ohio K9 unit of the Columbus Division of Police is evaluating where these officers fit into their plans going forward. The presumption of narcotics is that a dog hitting on an illegal substance would no longer be sufficient reason for a physical search. As such, sniffer dogs are only reliable to an extent, which means that there must be more indication for a full-blown search other than the K9 officer's response.

Dog sniffing facts

  • Dogs can distinguish scents that are masked by other scents due to a dogs' capability of smelling in layers.
  • Dogs are to date the best and most effective bomb detectors.
  • Trained drug-sniffing dogs can detect identical twins.
  • Marijuana and legal hemp smell the same to a K9 trained officer.
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