When Dr. Jen Gunter returned home from the grocery store she knew something was wrong with her normally boisterous 3-year-old Labrador retriever, Hazel.

“She was on the couch. Her head was hanging over and she couldn’t lift herself up,” Gunter, a gynecologist in Marin County, California, told NBC News. “I got out the tennis ball, which she ignored. Normally, you get out the tennis ball and she is just all over it.”

Hazel began shuddering when touched and couldn’t hold herself up or keep her eyes open. Then she lost control of her bladder.

“I thought 'Oh my god, my dog is dying from poison or she had a stroke,'” Gunter recalled.

Staff at the emergency veterinarian clinic immediately knew what was wrong.

“The nurse came over and said, ‘This looks like this could be marijuana poisoning; we see that all the time,’” Gunter said.

A urine toxicology text confirmed it: Hazel had THC in her system. Gutner suspects her dog accidentally ate an edible or a joint when on a run earlier that day.

Gunter posted the story on Facebook last week, urging people to properly store and discard their marijuana to protect their pets.

Calls to the Veterinary Services Poison Helpline about accidental marijuana ingestion in pets has surged 448 percent over the past six years, according to a statement provided by the American Veterinarian Medical Association.

Dogs are “very curious” and “indiscriminate eaters,” which means they’re more likely to wolf down a discarded joint, get into a bag marijuana flowers or gobble an edible, Laura Stern, a veterinarian with the ASPCA Animal Poison Control Center, told NBC News via email.

“We have seen a significant increase in the number of calls we have received about pets and marijuana,” said Stern.

Cats can also be harmed by marijuana, usually by exposure to second-hand smoke, but about 90 percent of the marijuana-related calls to the Animal Poison Control are about dogs, said Stern.

Peter Bowie, a veterinarian at Pet Emergency & Special Center of Marin, California, estimates he treats four or five dogs a week who have consumed marijuana.

“Treatment is supportive," he said. "If signs are moderately good, we do home nursing care. For more serious cases, we give IV fluids and do a respiratory watch."

Treatable, but dangerous

Dogs have larger concentrations of cannabinoid receptors — which are involved in memory, appetite and the sensation of pain — than humans, which make them “more susceptible to the effects of cannabis than people,” Gary Richter, a veterinarian at Holistic Veterinary Care in Oakland, California, told NBC News.

That’s why Richter urges people to call their vet if their dog has ingested any marijuana.

“People have a tendency to laugh it off and think it will be fine,” he said. “Find out what is recommended.”

Some dogs have seizures, or even become comatose. Cannabis may also cause dogs to have low heart rates, low body temperature, low blood pressure, tremors, or dilated pupils.

“The best way to compare it is to the idea of a really bad trip," said Bowie. "They are disoriented, hyper-reactive and they can also be somnolent. They stumble around and they pee on themselves."

More concentrated forms of THC — the psychoactive compound in marijuana — can have dramatic effects on dogs.

“The more THC a pet ingests, the more severe the signs generally are, so it takes a smaller amount of concentrated material — like edibles — to cause an issue than it would with plant material,” Stern said.

Marijuana toxicity can be treatable, so Bowie urges owners to tell a veterinarian if exposure is suspected.

"The more information you can give your veterinarian the better we can help your dog," said Bowie.

While most dogs recover, Richter has treated a dog that died from consuming marijuana. The dog slipped into a coma and it inhaled vomit into its lungs, causing sepsis and pneumonia, which led to its death.

Marijuana smoke can also cause dogs to get “contact buzzes” like humans and vets warn against against smoking marijuana when their pets are in the room.

Gunter's dog Hazel recovered from the ordeal, but Gunter is still shaken. Her Facebook warning has been widely shared.

“I am just trying to raise awareness,” she said.