A day before a scheduled vet appointment to euthanize her dog, Wendy Mansfield decided to try one last resort to alleviate the chronic pain of her 15-year-old labrador mix: cookies from a marijuana dispensary made specifically for ailing dogs.

Kali, a mild-mannered 80-pound rescue, was never much of a complainer. But she often licked her paws—an obvious sign of pain, according to her vet—which was typically accompanied by bouts of coughing because of the shedding fur that got in her throat. One cookie and 20 minutes later, the licking suddenly stopped.

Seeing this, Mansfield, who lives in Fort Bragg, California, gave her dog a second cookie, and then a third. Kali, who had been listless and depressed, got up to drink some water and walked outside—something she hadn’t been able to do recently without groaning or obvious signs of pain.

Mansfield then called the vet to cancel her appointment. That was three weeks ago. ”Never in my wildest dreams would I have anticipated this,” she tells Quartz. “It brought my dog back.”

With marijuana flourishing into a big business in the US, a new segment of the market catering to aging and ailing pets has been growing under the radar. The legal weed market raked in $2.7 billion in revenue in 2014, and one estimate by the ArcView Group, a network that connects investors with cannabis startups, projects the industry to top $10 billion in sales by 2018.

The pet-pot market is treading on new territory, however. The legal gray area is posing challenges for companies that want to market and distribute cannabis-derived products for animals. There’s also insufficient scientific backing and industry guidelines. Still, that’s not deterring desperate pet owners, like Mansfield, or keeping investors from getting on board.

The FDA is watching

The special cookies given to Kali were produced by Auntie Dolores, an Oakland-based maker of edible marijuana goods, including caramel corn, cheese crackers, and savory pretzels (a bestseller). The seven-year-old company launched its pet treat line, Treatibles, about a year ago.

Unlike its edibles for humans, Treatibles products, which are sold in dispensaries, aren’t made from marijuana but from hemp—the stem of the cannabis plant that’s low in the psychoactive component tetrahydrocannabinol, or THC, which produces that feeling of getting high. Hemp, however, does contain cannabidiol, or CBD, a chemical compound that alleviates pain. The US government also defines hemp as cannabis—not necessarily the stem—that measures less than 0.3% in THC, a threshold that allows its movement across state lines.

Most companies making cannabis-derived pet products choose to use hemp because the federal government still classifies marijuana as a Schedule 1 substance, defined as “drugs with no currently accepted medical use and a high potential for abuse.” Currently, 23 states and the District of Columbia have medical marijuana laws. But as it stands, veterinarians aren’t empowered to prescribe cannabis to pets. That could change soon. Nevada is currently debating a bill that would allow people to obtain medical marijuana for their pets with a vet’s approval.

Though Auntie Dolores CEO Julianna Carella has heard from customers like Mansfield, she’s hesitant to promote the product’s effects, or even market Treatibles at all. “Honestly, we’re hands off with that because we’re not doctors and it’s not our place to prescribe it in that way,” she says. The company’s also wary of attracting the attention of the US Food and Drug Administration, which recently began sending out warning letters to some companies selling cannabis-based products for animals.

One such recipient is Canna Companion, which in February got an ominous letter delivered to its headquarters outside Seattle saying that its product is an “unapproved new animal drug and your marketing of it violates the [Federal Food, Drug, and Cosmetic] Act.”

Sarah Brandon, an owner of Canna Companion, had no idea such rules existed. She and her husband have researched the effects of cannabis on pets for the past decade, stemming back to their days in veterinary school. In 2014, they took out a $20,000 loan to build a business selling ground hemp powder that dogs and cats consume orally.

They also used language on Canna Companion’s website and social media accounts that made the product sound like a drug, rather than a supplement, which the FDA noticed. This included phrases as innocuous as “safe and effective” and bolder claims like “reduce cancer-associated symptoms.”

“Being vets, we are required by law to use medical terminology,” Brandon says, explaining the original phrasing. “We don’t say an animal has tummy pains. We say they have gastritis and we use those terms.” But she understood the FDA’s point of view, and the company updated the language on its site and social media accounts.

Peak Pharmaceuticals has an exclusive licensing agreement to sell Canna-Pet products.

Canna-Pet, a Seattle company that sells capsules and biscuits for dogs made with hemp, received a similar letter from the agency. “It’s not an unusual thing for the supplement industry where the marketer is making claims that might be going too far,” admits Soren Mogelsvang, CEO of Peak Pharmaceuticals, which has an exclusive licensing agreement to sell Canna-Pet products. “We’re all a little guilty of that and were reprimanded by the FDA. We responded to the guidelines and adjusted our marketing materials accordingly.”

That said, the letter didn’t negatively impact sales. “If anything, it might have bumped it up a little,” he says. “Any PR is good PR.”

The role of THC

Some companies play it safe by using hemp, but Alison Ettel, CEO of San Francisco-based TreatWell (previously known as SweetLeaf), takes issue with the ingredient. She says companies that make cannabis-derived products for pets often source industrial-grade hemp, which is bred for fiber instead of medicinal properties.

Ettel only started using marijuana after she fell into a coma in 2011 due to complications from meningitis. In 2014, she created TreatWell with a grower in Humboldt County in California. About six months ago, Ettel, a former dog walker and animal shelter volunteer, began custom-making tinctures after desperate pet owners reached out directly to her. She also gave the concoctions to her own cat, who suffered from cancer and lived to be 15 years old before she was put down in January.

Treatwell

Industrial- and food-grade hemp is typically low in extractable cannabinoids. Multiple vets interviewed for this story say cannabis is most effective as a medicine when its full spectrum of cannabinoids (at least 85 have been identified) are deployed, even if they’re not as well studied as THC or CBD. Furthermore, Ettel says most industrial hemp is imported from overseas, where farming practices, such as the use of pesticides, might be more lax compared with the US. Though the marijuana industry can’t lay claim to the organic label, which is federally regulated, TreatWell prides itself on using marijuana grown following organic standards, she says.

Currently, there are no guidelines for marijuana’s use in dogs. But TreatWell believes THC shouldn’t be discounted, even if it draws scrutiny from the government. “What I’ll say is we target certain ratios for certain illnesses,” Ettel says. “I can’t make any claims it’ll cure anything.” Though results vary by individual animals, the company suggests a THC-to-CBD ratio of 1:1 for pain relief and appetite stimulation. A THC-to-CBD ratio of 3:1 is recommended for conditions associated with extreme arthritis, for example.

Because it’s operating in a legal gray area, TreatWell has avoided marketing its pet products and has taken extra precautions with distribution, selling directly to patients in California with medical marijuana cards that have joined its collective. The company also requires vet records from its members to prove their pets’ conditions are legitimate.

“There’s always going to be risk involved,” she says. “To be honest, helping these pets and these people is much more important to me.”

Undeterred investors

Despite the risks, investor interest hasn’t subsided. TreatWell hasn’t taken any outside funding to date, but it’s currently in the process of raising money from investors so it can produce tinctures for pets with standardized dosing and sell them in dispensaries. ”[Investors] already swallowed that pill,” says Ettel. “They wouldn’t be there if they weren’t comfortable with cannabis.”

That’s the case with Doug Leighton at Dutchess Capital, a marijuana-focused investment firm in Boston. “I’m already in this space anyway,” he says. He’s also not concerned about the challenges of selling the product because ”the dog is not going to go to jail,” he adds.

One of the firm’s investments is in Dixie Elixirs and Edibles, which Leighton says is developing a line for pets. The company, which makes cannabis-infused drinks, treats, and lotions, declined to be interviewed for this story. A representative said it was too early to talk about its plans for the pet market.

Because the cannabis market for pets is so new, others are treading lightly. “The potential issues around politics and legislation are always a concern in the cannabis space,” says Emily Paxhia, a partner at Poseidon Asset Management, an investment firm in the marijuana industry. Still, she can’t deny the ”massive market potential” since it sits at the intersection of two billion-dollar industries: pot and pets. In total, investors, including Poseidon, have injected $800,000 into Auntie Dolores so far.

Paxhia saw how Treatibles helped her own dog, Sprout, a three-legged terrier mix. She says the treats have helped reduce Sprout’s inflammation, caused by the additional stress put on her front leg, and calmed her anxiety.

Treatibles is still only a small fraction of Auntie Dolores’s business, having sold about 1,100 units thus far. To provide some context, Carella, who declined to disclose revenue figures, says the company “sold almost a quarter of a million units last year with all our products combined.” The edible goods maker is looking to raise an additional $1.25 million to scale its operations, and it’s in the process of spinning off Treatibles as its own entity, so investors can choose to put their money into either or both businesses.

Scientific backing

Veterinarians are only staring to learn about marijuana’s effects on animals. In March, the California Veterinary Medical Association held a conference in Yosemite National Park where one of the major themes was cannabis.

Dawn Boothe, who teaches at Auburn University’s College of Veterinary Medicine in Alabama, presented on the topic, but admits there’s much that’s unknown. “If you want to back up and have a discussion about the scientific evidence on the use of medical marijuana in dogs, we’re done because there isn’t any,” she says. Prior studies have found, however, that cannabinoid receptors are present in mammals, birds, reptiles, and fish.

Her department recently submitted a grant application to the Morris Animal Foundation, a nonprofit organization that funds scientific studies for animals, to conduct research on cannabinoids’ effects on dogs.

Peak Pharmaceuticals, which has a lab at the University of Colorado in Denver, is also doing its own research. It’s partnered with a vet hospital to conduct clinical studies on the effects of cannabinoids on dogs with epilepsy. The company has also struck an agreement with a university to study the effects of cannabinoids on horses that suffer from joint pain and anxiety.

“If you think about it, universities are still in limbo,” says Mogelsvang, who contractually couldn’t name the company’s research partners yet. “They don’t know if they can research cannabinoids and are worried about losing grant funding. The hemp laws, the farm bills—there’s very little case law that defines what’s right and what’s wrong.

Though Boothe knows the evidence is lacking, she points to past marijuana studies done on lab animals and existing human drugs on the market that contain cannabinoids. One such example is Sativex, a mouth spray prescribed in Europe that controls symptoms associated with multiple sclerosis. It lists THC and CBD as active ingredients. “We can’t ignore the therapeutic benefits,” she says.

That said, she’s extremely wary of hemp-based pet products on the market, especially since there’s so little oversight for supplements.

Many players in the marijuana industry are hoping new research will shed light on cannabis’s effectiveness in pets and help the industry set guidelines on quality and dosage. (The companies interviewed for this story offer suggestions based on the animal’s weight, recommending pet owners start with a lower dose and gradually increase the amount as needed.)

Playing doctor

What Boothe is most concerned about is pet owners making health decisions without the guidance of a vet. “I’d like to think that people would think it’s a bad idea to treat children without a physician’s advice,” she says. “I think it’s the same with animals.”

Even Brandon of Canna Companion agrees. “As a business owner, pet parent, and veterinarian, I absolutely understand that desperation people feel,” she says. “They feel this beloved member of their family is suffering and they don’t know how to help them.”

But she strongly urges pet owners to consult their vets before taking their animals off prescribed drugs. Suddenly stopping some anti-convulsive medications could make their dogs seriously ill, she says, as an example.

Wendy Mansfield never consulted a professional before giving Kali those cookies. Her vet, however, was open-minded about the alternative treatment and asked Mansfield to periodically check in.

Mansfield also reduced the number of drugs Kali takes now. Instead of taking four pills, two of them narcotics, Kali now gets three to four cookies every few hours and a pain blocker to help her sleep at night. ”[Vets] are in a strange position, and this is all new,” she says. “The best way to gauge your dog is to watch them. With my involvement with my dog, my vet feels comfortable with my decision.”

Mansfield, who suffers from Bell’s Palsy, chose the same alternative for herself four years ago as she recovered from the effects of meningitis, encephalitis, and a medically-induced coma. Her doctor had prescribed her oxycodone, a narcotic pain killer, but Mansfield was adamant against it, choosing instead to self medicate with marijuana. “I never took one of those pills—never, never, never.”

She can’t help but see the parallel between her and Kali’s lives. “I’m a walking miracle, too,” she says.