Little Kitty doesn’t hide anymore. In fact, she’s more like her old self: sunbathing on the living room carpet, playing with Ms. Mastramico’s other cat, Valentina. “When I’ve given it to her, she’s never acted high: falling face-first into her food bowl, chowing down,” Ms. Mastramico said. “She comes out and socializes, wants to be in your lap, wants to be petted. It’s a very noticeable difference.”

Other animal lovers who have turned to cannabis-based products to alleviate a host of pet maladies, including seizures, inflammation, anxiety and pain, are reporting similar results. Although they have not been approved by regulators, marijuana-based treatments are being used not only for cats and dogs, but for pigs, horses and domesticated wild animals.

Maria Ellis Perez, 55, a mold inspector from Pompano Beach, Fla., gives Treatibles chews made from hemp to one of her pets, a domesticated female skunk named Ricochet. At age 12, Ricochet limps and has cataracts. At one point, she had grown so withdrawn that she refused to eat. “We thought it was her time,” Ms. Ellis Perez said.

But after a few days of nibbling hemp, Ricochet seemed more content. “She was turning her head and looking up with the good eye,” Ms. Ellis Perez said. “She showed up for breakfast.”

The Food and Drug Administration has not approved cannabis for pets, in part because there is little research showing its effectiveness. Veterinarians are not allowed to write prescriptions for the products and, in states where marijuana is illegal, are wary of discussing the idea. Last year, a proposed state law was defeated in Nevada that would have made it possible for veterinarians to prescribe cannabis to pets with chronic illnesses. Still, users swear by the products.