The U.S. Food and Drug Administration issued a warning Wednesday about the proliferation of untested pot, cannabis and marijuana-based products being marketed as treatment or cures for cancer.

The FDA put out a statement Wednesday saying they issued warning letters to four companies that are illegally selling products online that claim to “prevent, diagnose, treat, or cure cancer without evidence to support these outcomes.” The agency cautions that companies marketing unsubstantiated therapeutic claims are a violation of the Federal Food, Drug and Cosmetic Act in addition to putting patients in dire risk of worsening symptoms.

A recent study found that opioid-related deaths in Colorado have fallen 6 percent since the state legalized recreational marijuana.

The agency says it has issued more than 90 warning letters in the past decade – including more than a dozen in 2017 – to companies marketing hundreds of fraudulent pot products. Several websites and social media advertisements make promises that weed-infused products contain miracle-like cancer-curing relief.

“We have an obligation to provide caregivers and patients with the confidence that drugs making cancer treatment claims have been carefully evaluated for safety, efficacy, and quality, and are monitored by the FDA once they’re on the market,” FDA Commissioner Scott Gottlieb writes in the statement.

“We recognize that there’s interest in developing therapies from marijuana and its components, but the safest way for this to occur is through the drug approval process – not through unsubstantiated claims made on a website. We support sound, scientifically-based research using components derived from marijuana, and we’ll continue to work with product developers who are interested in bringing safe, effective, and quality products to market,” Gottlieb added.

A study and anonymous survey conducted by the Fred Hutchinson Cancer Research Center of 2,737 eligible patients at the Seattle Cancer Center Alliance this year found that two-thirds (66 percent) reporting they had previously used marijuana. One-quarter said they used it in the past year and just slightly less reported smoking or ingesting a marijuana product in the past month. The study published in the journal Cancer found that patients were using marijuana to help treat symptoms including pain, nausea, upset stomach and stress stemming from cancer.

Dr. Junella Chin, an osteopath and integrative cannabis physician, tells Healthline that many cancer patients simply run out of options and give up on prescribed medicines to alleviate symptoms – that’s when they turn to pot products.

“And when these don’t work, or they are too taxing on their system, they research cannabis as an option, legal or not,” said Chin.

Chin says cannabis is the only anti-nausea medicine that increases appetite, assists patients’ sleep cycles, eases pain, and elevates their overall mood.

But according to the FDA’s Nov. 1 health warning, cancer patients should be weary of potentially false marketing campaigns found through the internet or otherwise.

“Substances that contain components of marijuana will be treated like any other products that make unproven claims to shrink cancer tumors. We don’t let companies market products that deliberately prey on sick people with baseless claims that their substance can shrink or cure cancer and we’re not going to look the other way on enforcing these principles when it comes to marijuana-containing products,” said FDA Commissioner Scott Gottlieb, M.D.

“There are a growing number of effective therapies for many cancers. When people are allowed to illegally market agents that deliver no established benefit they may steer patients away from products that have proven, anti-tumor effects that could extend lives,” Gottlieb added in the statement.