As an emergency hospital veterinarian in California, Dr. Tracey Hanna saw an average of one dog a day intoxicated by marijuana. That’s right, every day. During pot harvest season, the rate rose to about one stoned dog per hour. The typical patient would stagger, act dopey yet nervous and dribble urine. The rare patient would be comatose.

Hanna practiced from 2009 until the middle of this year in Sonoma County, a region that, along with Mendocino and Humboldt counties on the Northern California coast, is known for marijuana cultivation.

“Our running joke was that if people weren’t growing grapes for wine, they were growing weed,” Hanna said. “The vast majority of exposures I saw there were dogs that got into plants outside — not so much that they got into the owner’s stash, although that happened, too.” Fortunately in most cases, patients could sleep off the effects.

The number of marijuana cases Hanna saw is unusual but the act of dogs eating food made from the the plant, or plant itself — Cannabis sativa, which contains the psychoactive ingredient tetrahydrocannabinol (THC)  — is not new. It was the topic of an article in the Journal of the American Veterinary Medical Association, “Acute oral marijuana poisoning in the dog,” published in November 1979.

Here's what's new: The number of recorded cases of dogs consuming marijuana is rising. The increase comes as changes in state laws allow more Americans to take the drug as medicine. The Animal Poison Control Center operated by the American Society for the Prevention of Cruelty to Animals (ASPCA) logged 309 calls in 2011 about dogs eating marijuana, more than triple the number of calls 10 years earlier.

Similarly, a study scheduled for publication in an upcoming edition of the Journal of Veterinary Emergency and Critical Care documents a fourfold increase in marijuana toxicosis cases among dogs seen in two Colorado veterinary hospitals between January 2005 and October 2010. In the same period, the number of Coloradans registered for medical marijuana rose by a factor of 146.

While it’s not clear that legal medical marijuana use is driving accidental exposures in pets, the trend nevertheless begs the question: Will stoned dogs become more common when the law permits recreational marijuana use?

Voters in Colorado and Washington this month made it legal for people 21 and older to possess up to an ounce of marijuana. Decriminalization in Colorado takes effect once the vote is certified (generally about a month after the election). In Washington, the law takes effect Dec. 6.

Dr. Elizabeth Davidow, a veterinarian board-certified in emergency and critical care, has seen her share of marijuana-poisoning cases at the 24-hour emergency hospital she co-owns in Seattle. The frequency rose noticeably in the past two years, she said, corresponding to the establishment of three medicinal pot dispensaries within two miles of the hospital.

“For a period of time this year, we had a pot case every week,” Davidow recalled. “What’s weird is, nobody says, ‘I’m on medicinal pot because I have this disease.’ People will say, ‘Yes, there’s pot in the house,’ or ‘There was a pot brownie,’ or ‘My dog got into something behind a tree at the park.’ ”

Although Davidow has observed what seems to be a relationship between the availability of medical marijuana and accidental exposures in dogs, she’s not convinced decriminalization of casual use will drive up cases further.

“I think there’s a ton of it out there (already),” she said. “I think the state is finally going to get the tax revenue from it.”

Davidow suspects the new law reflects a relaxed attitude toward marijuana that’s already a part of the culture of the region. “I think people haven’t been scared (for some time) to say that it’s pot, and it’s around,” she said.

That’s a change from the past. On the Veterinary Information Network (VIN), an online community for the profession, many members discussing suspected marijuana toxicosis have in the past focused on how to help owners feel safe acknowledging that their pets had access to marijuana so the doctors could treat exposures appropriately. The spreading acceptance of cannabis as legitimate medicine may render such conversations unnecessary.

California was the first state, in 1996, to make marijuana legal as medicine. Alaska, Oregon and Washington followed in 1998. Today, 18 states plus the District of Columbia permit it, according to ProCon.org, a nonprofit, nonpartisan organization that examines public-policy issues.

Dogs don’t eat pot only where marijuana is allowed as medicine, of course. Calls to the Animal Poison Control Center about pot last year came from 33 states, including Florida, Georgia, Texas and other jurisdictions where marijuana is prohibited completely.

VIN members posting about cases of pets ingesting marijuana sometimes noted that they worked in or near a college town.

While the occasional cat is known to get into marijuana, by all accounts, the vast majority of veterinary patients are dogs. The Animal Poison Control Center records for marijuana calls received in 2011 involve everything from a quarter-pound Yorkshire terrier puppy to a 109-pound adult Great Dane.

So common apparently is the phenomenon of dogs getting into pot that more than one veterinary practice devotes space on its website to the topic.

In 2011, Veterinary Practice News published an article titled “Treating Marijuana Toxicity” by Dr. Patrick Mahaney, a California practitioner.

Mahaney told the VIN News Service by email that he saw somewhere between 30 to 40 cases while answering emergency calls in the five years from 2006 to 2011. “The practice was in West Hollywood, where there are plenty of marijuana dispensaries (and celebrities actively using the product),” he said.

A video clip that Mahaney posted on YouTube and provided to the VIN News Service shows how one Italian greyhound intoxicated by marijuana behaves. Looking about with wide eyes, the dog wobbles on its long, thin legs, struggling to keep its balance. Finally, it gives up and lies down.

Doctors familiar with the hallmarks of marijuana exposure in dogs say ataxia, or loss of body control, difficulty walking, disorientation, lethargy, slow reflexes and hypersensitivity to touch or sound are common clinical signs — similar to what you’d expect in a person under the influence. Another typical sign in dogs is urinary incontinence, which fortunately is not typical of people high on pot.

Veterinary treatment might involve inducing vomiting and administering a liquid form of activated charcoal, which binds the toxicant, helping the body to excrete it more efficiently. Many patients are sent home afterward to sleep off residual effects of the drug.

Serious cases of intoxication, such as when a patient has an extremely low heart rate or can’t swallow or stand, require a hospital stay and intravenous fluids. Doctors might use intravenous lipid therapy to draw out the THC, a substance attracted to fats. In rare instances, patients may be unconscious for many hours.

Hanna, the veterinarian who saw stoned dogs daily at a Northern California emergency hospital, said she’s seen some “out cold, sometimes for more than a day.” The worst case she saw was that of a big, black Labrador retriever who’d eaten butter infused with marijuana. The Lab was basically comatose. He needed a urinary catheter, and staff would roll him over every four hours to avoid circulation problems.

“Three days later,” Hanna said, “he got up.” The Lab was back to normal.

A pet dying from eating marijuana is extremely rare but not unheard of. Doctors at Wheat Ridge Veterinary Specialists, an emergency and referral hospital near Denver, Colo., saw two patients die in 2010 following marijuana exposure. The first, a 9-year-old male Schipperke, ate a half-dozen chocolate chip cookies baked with butter infused with THC extracted from marijuana. His owner found him comatose. He died at the hospital 40 hours later.

The second patient was a 7-year-old female cocker spaniel who ate half a pan of brownies containing THC-infused butter. She, too, was comatose, and went into cardiac and respiratory arrest 10 hours after being taken to the hospital. She died four hours later.

Dr. Stacy Meola, who tried to save the cocker spaniel, was spurred by the deaths to take a closer look at marijuana toxicosis. She sensed that the number of cases had gone up since she began practicing emergency medicine in Colorado in 2006. Searching the hospital’s database confirmed her hunch.

To check whether the hospital’s experience was unusual, Meola looked at cases seen at the veterinary hospital of her alma mater, Colorado State University in Fort Collins. Same there. Together, the number of cases quadrupled between 2005 and 2010.

It wasn't a matter of the hospitals simply getting busier. At Wheat Ridge, the number of marijuana toxicosis cases rose from 1.5 per 1,000 emergency cases seen in 2005 to 4.5 per 1,000 five years later.

At Colorado State, the increase was 0.16 per 1,000 to .81 per 1,000 in the same period.

Meola also examined the number of Coloradans registered for medical marijuana identification cards. In the same five years, the population of registrants rose from 730 to 106,653 — a factor of 146.

The findings, accepted for publication in the Journal of Veterinary Emergency and Critical Care, led Meola and her four co-authors to conclude: “As medical marijuana becomes more available to the general population, an increase in the number and severity of marijuana toxicity cases may also be seen in companion animals. Dogs ingesting medical-grade marijuana butter products may be at higher risk of serious complications, and earlier aggressive treatment may be warranted.”

At the same time, the researchers acknowledge that the increased number of cases may be driven by factors others than the growing popularity of medical marijuana. It could be that veterinarians are simply more aware of the possibility that a patient may have been exposed to marijuana, and that THC toxicity was underdiagnosed in the past. Or perhaps clients are more willing today to seek medical attention for their dogs and to admit that their dogs had access to pot.

To the degree that changing laws make marijuana more readily accessible to people, though, it’s probable that marijuana will be more accessible to their pets, Meola said. “I do think there’s a potential for greater exposure to it,” she said. “Dogs are fairly cunning and they’ll eat just about everything.”

On the other hand, if greater access brings greater awareness, the opposite could be true, suggested Davidow, the emergency medicine specialist in Seattle.

Supposing pet owners learn about animals’ propensity to get into the stuff, perhaps they’ll do a better job keeping it out of reach, she said: “The one thing about legalization, if there is more education around it, then people will know.”