A product called Poppy Seed Wash is advertised as a natural alternative to opioids for relaxation and pain relief, but it’s really just an unlicensed drug, the Food and Drug Administration said Tuesday.

The FDA posted a warning letter to the makers of the product, telling them to stop making medical claims and to stop selling it online.

“Your Poppy Seed Wash product is not generally recognized as safe and effective for the above referenced use and, therefore, the product is a ‘new drug,'” the FDA says in its letter.

The internet is awash in sites offering “natural” alternatives to opioids, and the FDA has been trying to shut down those that are offering potentially dangerous products, such as the kratom plant.

Poppy Seed Wash is a beverage, generically known as poppy seed tea. The FDA classifies it as an unlicensed drug.

Poppy seeds can be a source of opiates. They don’t contain opiates themselves, but the pod of the plant they develop in does. Most of the seeds used in food are washed for this reason — washing removes any residue of the opiate-containing poppy fluid.

People who eat poppy seed bagels or muffins can fail drug tests.

But do-it-yourselfers trade tips on how to get unwashed seeds and use them to make tea or, in this case, a wash that they hope will contain enough opiate to have an effect. Poppy seeds themselves are legal for sale in the U.S.

The PoppySeed Wash site (it spells the product name both ways) sells a kit that includes poppy seeds and a bottle to mix them with water and wash off any residue. Drinking this “wash” can ease pain, the site claims.

“The opioids relax and sedate the body,” the site promises. “PoppySeed Wash relieves anxiety by slowing down the central nervous system and has a relaxing and calming effect on the mind and body. Because it works quickly, it can be effective during a panic attack or another overwhelming anxiety episode.”

These are medical claims, the FDA said, and must go through a formal approval process.

“The claims on your product label and websites establish the product is a drug" because it is "intended for use in the cure, mitigation, treatment or prevention of disease,’ the warning letter reads.

“FDA approves a new drug on the basis of scientific data and information demonstrating that the drug is safe and effective.”

An hour after the FDA notice became public, the site appeared to have been altered, with references to opioids and to any potential effects of the product removed.

Testimonials on the site make it clear that buyers believe they are getting a safer, somehow more “natural” product.

“I am kind of a hippie and don't really trust all the chemicals and pharmaceuticals out there that companies and doctors are always trying to sell,” reads one testimonial.

“I prefer natural substances that god made. The problem is that most 'natural' remedies like elm bark, turmeric, passion flower, twigs, leaves and newt eye don't really work. I love Poppy Seed Wash because it is all natural, organic and it actually works!"

But the FDA said there is no way to direct the safe use of Poppy Seed Wash.

“Your PoppySeed Wash product is intended for treatment of one or more diseases that are not amenable to self-diagnosis or treatment without the supervision of a licensed practitioner," it said.

“Therefore, it is impossible to write adequate directions for use for a layperson to use your product safely for its intended purposes.”

The FDA letter addresses the legal basis of the claims, but any product containing opiates can be dangerous.

Earlier this year, Betty and Steve Hacala of Rogers, Arkansas, met with members of Congress and the FDA after their son, Stephen, died. He had morphine in his blood and a bag of poppy seeds, as well as a water bottle filled with seeds, was found near his body, according to numerous media reports.

“Stephen's death resulted in part because of a dangerous gap in our nation's drug laws. It's been well known for ages that poppies are dangerous, both addictive and toxic,” Senator Tom Cotton, R-Ark., said in April.

“That's why it's illegal to grow or own almost any part of the poppy — the straw, the pod, the latex. But there's an exception, of course, for poppy seeds, which many people enjoy on bagels, muffins, cakes and other pastries.”

Tests of poppy seed washes and teas have shown that they can deliver both morphine and codeine.

Cotton said Walmart and Amazon had agreed to stop selling unwashed poppy seeds online.

The Poppy Seed Wash company, which doesn’t provide a physical address, did not respond to requests for comment from NBC News.