Veterinarians say they're seeing an increasing number of dogs sickened after ingesting marijuana, and are warning pet owners to take care as Canada prepares for cannabis legalization this year.

Dr. Jeff Goodall, a veterinarian who runs the Sunnyview Animal Centre in Bedford, N.S., said he's seeing a growing number of dogs with marijuana toxicity.

"It profoundly affects the neurological system. It can progress to tremors and seizures, and they can go into a coma," he said Tuesday.

Goodall said his Halifax-area clinic saw five cases in 2017, three in 2016, and none the year before that.

He said the tetrahydrocannabinol or THC in marijuana doesn't make dogs high. Rather, it makes them very sick.

"The THCs are very toxic to pets in the sense that they cause profound levels of confusion, then the dogs start to cry or vocalize and become hyperactive. They get through that period fairly quickly and then they begin to drool and become unable to walk properly," Goodall said.

"By the time they're in the clinic it's very clear that they have marijuana toxicity because the poor dogs have excessive or uncontrolled urination."

In rare cases it can lead to death.

Goodall said in four of the five cases he saw last year, the owners were upfront about the cause of their dog's illness and they were able to proceed quickly with treatment.

However he said the owner in the fifth case was in denial.

"She was accusing us of accusing her children of using recreational medication, when that wasn't what we were saying at all. We were just saying, this is what the dog has," he said.

Goodall said cannabis edibles are also harmful to dogs.

"One of our cases this year was cannabis-containing brownies. We also had another dog who ate a bag of suckers. The problem there wasn't the cannabis, it was the xylitol. Xylitol is an artificial sweetener often used in sugar-free gum, and it is extremely concerning to pets," he said.

Goodall said he'd like to see warnings and greater public education on what marijuana can do to pets.

In Colorado, where recreational marijuana was legalized in 2012, there was a four-fold increase in reported cases of toxicity in dogs between 2010 and 2015.

An article posted on the website of the Canadian Veterinary Medical Association says dogs are proportionally more sensitive to the active compounds in marijuana than people, and in small dogs, excessive intake can easily result in signs of toxicity.

It also says that cats are not immune to the toxic side effects but are more selective in what they eat. They also lack the sweet tooth that would make cannabis edibles as attractive as they are to dogs.

Goodall said there are other components in cannabis that may eventually prove useful in treating some symptoms and illnesses in pets, but more research needs to be done.

The Canadian Veterinary Medical Association says for now, marijuana is not approved for medicinal use in animals.

"Giving products to your pet may have unknown side effects and unproven effectiveness. Especially exposing them to THC-rich recreational marijuana could put them in a life-threatening medical crisis," its article states.