San Francisco veterinarian Jill Chase had just finished hosting a birthday party for her son 10 years ago when her dog went limp. After investigating what might have caused the problem, she discovered the culprit: cannabis-infused butter that a neighbor had dumped in the garbage down the street. Her dog, a Tibetan terrier who was a habitual trash surfer, had eaten a large dose.

"He was completely ODd in a coma for three days, on my bathroom floor with an IV," said Chase, whose dog eventually recovered.

Since Chase's experience, cases of marijuana poisoning in dogs have increased, particularly in states like California where medical marijuana is legal. As one veterinarian put it, our dogs are "munching out." Dogs are known to be indiscriminate eaters, going after paper, trash, random objects on the street and, now, their best friend's cannabis.

The Pet Poison Hotline, which takes calls from around the country and Canada, noted a 200 percent increase in reported incidents of poisoning in the past five years. Dr. Lori Green, a critical care veterinarian at the San Francisco SPCA Veterinary Hospital, says the clinic treats as many as three dogs a week for symptoms of marijuana toxicity: trembling, vomiting and walking troubles.

"There's been an increase as marijuana becomes more acceptable in public and less of an underworld thing," said Dr. Karl Jandrey, an assistant clinical professor at the UC Davis School of Veterinary Medicine, where the animal hospital treated 27 dogs for pot poisoning in the past year, up from four in 2010.

Pot's effect different on dogs

A study published in the Journal of Veterinary Emergency and Critical Care in 2012 reported a correlation between the increase in the number of medical marijuana cardholders and the number of dogs getting poisoned. The study found a fourfold increase in cases seen at two Colorado hospitals over six years. All but two dogs - who ate cannabis butter - survived.

If only a small amount of marijuana is consumed, dogs may become listless or depressed. Pot affects dogs differently than it does humans, veterinarians say, because dogs don't have liver enzymes to metabolize tetrahydrocannabinol, or THC, the active ingredient in cannabis. At higher doses, marijuana can cause dogs to vomit, lose coordination and bladder control, have tremors, and be nervous and over-reactive. Their body temperature and heart rate may drop.

In extreme cases dogs may suffer seizures or seem unresponsive, but THC poisoning is rarely fatal. Dogs usually recover in 12 to 24 hours, though signs can last up to 72 hours.

"We had one dog affected for three days, but it turns out there was psilocybin and antidepressant in the brownie," Green said. "It was a healthy young dog, but it got the whole cocktail."

Few poisonings fatal

A urine test can determine if THC is present, but most dogs are diagnosed based on symptoms, which veterinarians say makes it hard to document the exact number of cases. While many owners take dogs to the veterinarian, an unknown number of others call for advice, consult the Internet or wait out the symptoms at home.

A 2002 study by the American SPCA's Animal Poison Control Center of 250 cases of accidental marijuana ingestion found that only two were fatal - to a cat and a horse. The vast majority of the poisonings, 96 percent, occurred in dogs, with 3 percent in cats and the remaining 1 percent in other species, according to the ASPCA, which also runs a poison hotline.

Veterinarians report that some people give their animals marijuana vapors, tinctures or edibles for pain control, and trade pot biscuit recipes on the Internet and discuss dosage. Green and others discourage such treatment, saying there are more effective, safer drugs available and that there is insufficient research showing that pot helps relieve pet suffering.

Most people who know how their pet got sick are up-front about it, Green said, but sometimes they don't know. Or they don't want anyone else to know. She recalls one client who admitted, after her teenage daughter left the room, that it was her own stash.

"We make it clear we're trying to help the dog and not pointing the finger at anybody," she said. "The dog might have gotten it from a park or a trash can or from a buddy's backpack."

Emergency care

Veterinarians say it's important to get emergency treatment for dogs that show symptoms of THC toxicity, which usually show up 30 to 90 minutes after ingestion. Treatment may include inducing vomiting, or, if the dog is too woozy, feeding it activated charcoal to absorb what's in the stomach. In some cases, the dog might need intravenous fluids to help flush out the toxins and an overnight stay for close monitoring of vital signs.

The bill for treatment can vary from a few hundred dollars to more than $1,000, depending on the level of care needed.

Green advises being vigilant about what might put pets at risk, particularly during the season when marijuana edibles may be on the holiday menu.

"Be aware that it might not be your animal but someone else's," she said. "They will eat anything you leave out."