Federal regulators Tuesday warned Curaleaf, one of the nation’s largest cannabis companies, to stop marketing CBD products online with unfounded claims that they treat cancer, Alzheimer’s disease, opioid withdrawal, pain, and pet anxiety.

The US Food and Drug Administration said Curaleaf, based in Wakefield, was “illegally selling” more than a dozen products containing CBD — cannabidiol, a nonpsychoactive compound in cannabis — using unsupported claims such as “CBD was effective in killing human breast cancer cells.”

The FDA said the claims on social media and the company’s website could endanger patients who might choose to delay seeking medical care. The FDA has sent similar warning letters to about two dozen CBD companies since 2015, but the Tuesday letter shook the industry because of Curaleaf’s size.