Cannabidiol holds a certain mystique, but CBD coffee might not be the best place to get it.

From oat milk and rose lattes to those crazy unicorn drinks at Starbucks a few years ago, it seems coffee shops are always among the first to jump on the latest drink trends. The newest offering: CBD coffee, or cannabidiol that's added to plain coffee or blended into a latte. (Psst—here’s exactly what CBD is, in case you’re wondering.)

When Dan Guy, owner of Espresso Bay coffee shop and roastery in downtown Traverse City, Michigan, debuted a CBD latte last month, he hadn’t anticipated just how buzzy it would be.

“Since we started, a quarter to a third of our customers [have upgraded to] CBD drinks,” he says. “I knew it would be popular, but didn’t expect it to take off so fast.”

Guy has a personal reason for adding CBD coffee drinks to the menu. About five years ago, he was diagnosed with an autoimmune disease that causes him chronic pain in his legs. After trying nearly everything out there, including serious painkillers he didn’t want to be on, someone told him about CBD oil. He consumed it in capsule form for a few days and noticed his pain starting to dull. Since then, he’s taken it alongside his morning coffee every day—and decided to offer his customers the same kind of experience.

“It’s the perfect combination, because the CBD oil can make you a little drowsy, so drinking it with your coffee kind of balances it out,” says Guy. “You feel a nice, natural peacefulness while still feeling alert.”

The CBD latte at Espresso Bay is made with steamed milk, espresso, CBD oil, and a little honey and cinnamon. Though the oil itself is unflavored, it tends to “kind of taste like a plant,” says Guy, so the honey and cinnamon mask the flavor and add a touch of sweetness. Customers also have the option to add CBD oil to any drink, from hot chocolate to tea to smoothies; amounts run from 5, 10 or 15 milligrams for $2, $3 or $4. Surprisingly, few people have commented on the price, Guy says, even though a drink can easily run upward of $6 or more with an add-on.

But just because something is trendy doesn’t mean it’s right for everyone. While CBD oil has been shown to be effective in treating certain epilepsy patients in several clinical trials—and is purported to treat conditions ranging from anxiety and depression to autoimmune disorders, and even cancer—more research is needed to prove what it can actually do.

“I think we just don’t have enough literature yet,” says Kimberly M. Mauer, M.D., medical director of OHSU’s Comprehensive Pain Center in Portland, Oregon. “It’s something we’re studying [to help with] pain and its inflammatory properties.”

It also goes without saying that baristas aren’t physicians—and as such, shouldn’t be recommending CBD oil, or any supplement for that matter, to customers. One reason for this: The sourcing of CBD oil has major issues.

“The problem is that [CBD oil] is a nutraceutical, like a supplement,” says Peter Grinspoon, M.D., a Boston-based Harvard Medical School instructor and board member with Doctors for Cannabis Regulation. This means it’s not regulated by the FDA, so when you buy it online you really have no idea what you’re getting.

A 2017 study examining labeling accuracy of CBD extracts sold online revealed serious discrepancies. Of the 84 products tested, 26 percent contained less CBD than they claimed on the label (read: they’d likely be ineffective, so a waste of money). More worrisome: 21 percent of the samples contained traces of THC, the chemical compound in cannabis that gets you high—and could cause you to test positive on a drug test. (Yikes!)

In January, New York City’s Health Department began embargoing cannabidiol-infused food and drinks, and ordered all restaurants, cafes, and bars in the area to stop selling them this week. They said the order will continue until CBD is deemed “safe” as a food additive. A spokesperson told CNBC in an email, "The Health Department takes seriously its responsibility to protect New Yorkers' health. Until cannabidiol (CBD) is deemed safe as a food additive, the Department is ordering restaurants not to offer products containing CBD."

It's unclear whether other cities will follow suit, but Dr. Grinspoon still doesn’t think adding CBD to your coffee is the worst thing you can do. “Generally speaking, CBD is a very safe medication, and if it helps people relax, it’s totally fine,” he says.

Instead of relying on your coffee shop for CBD, it’s wise to purchase your own CBD oil and add it yourself, he says. If you do your homework, you can guarantee it’s from a reputable source and control how much you’re getting. You should look for quality certifications where the product has been sent to an outside lab and verified that it actually contains the amount of CBD oil it promises.

“If you buy aspirin, you’re getting aspirin,” says Dr. Grinspoon, “but if you buy CBD, you have to do research to make sure you’re getting right dose and amount.”

At a coffee shop offering CBD add-ons in Chicago, we quizzed the barista about the dosage, to which she replied, “somewhere around 200 milligrams, I think?”—a dosage that would be way over what someone would typically want to consume, proving the point.

If you do fork over the cash for a coffee shop CBD latte (just for fun!) there’s probably no harm in simply trying it, says Dr. Greenspoon. But to be safe, first have a conversation with your primary care physician about how it could benefit you, says Dr. Mauer, and also be aware that any effects you do experience could be placebos, too.