23andMe, the Google-backed DNA analysis company co-founded by Anne Wojcicki, was told by U.S. regulators to halt sales of its main product because it’s being sold without “marketing clearance or approval.”

The Saliva Collection Kit and Personal Genome Service, or PGS, tells users whether they carry a disease, are at risk of a disease and would respond to a drug. Most of the uses fall into the category of a medical device and require Food and Drug Administration approval, the agency told the California-based company in a Nov. 22 letter made public today.

The FDA said the company has failed to show that the technology is supported by science.

In a warning letter posted online Monday, FDA regulators say that the Silicon Valley firm has not shown that its tests are safe or effective despite “more than 14 face-to-face and teleconference meetings” and “hundreds of email exchanges.” The agency orders 23andMe to stop marketing its test immediately, warning that erroneous results could cause customers to seek unnecessary or ineffective medical care.

Wojcicki, who recently separated from her husband, Google co-founder Sergey Brin, started 23andMe about six years ago to help people assess their risk of cancer, heart disease and other medical conditions. Brin used the saliva kit to determine he had a gene that makes him susceptible to Parkinson’s.

“FDA is concerned about the public health consequences of inaccurate results from the PGS device,” the agency said. “The main purpose of compliance with FDA’s regulatory requirements is to ensure that the tests work.”

The FDA decided in 2010 that services claiming to evaluate a customer’s risk of disease must be cleared by regulators if the companies sell directly to consumers. Most FDA-cleared genetic tests are for a single disease while 23andMe’s would be the first to test for multiple conditions.

“We recognize that we have not met the FDA’s expectations regarding timeline and communication regarding our submission,” Catherine Afarian, a spokeswoman for 23andMe said in an email. “Our relationship with the FDA is extremely important to us and we are committed to fully engaging with them to address their concerns.”

23andMe submitted FDA applications in July and September of 2012 for the least stringent of two types of medical device reviews. The FDA said the company failed to address “the issues described during previous interactions.”

UnitedHealth Group, the largest publicly traded U.S. health insurer, raised concern in a March 2012 report about the accuracy and affordability of the tests. Such types of genetic tests may become a $25 billion annual market in the U.S. within a decade, highlighting the need to identify which work best, the insurer said at the time.

For years, 23andMe resisted government regulation, arguing that it simply provides consumers with information, not a medical service. But last year the company changed course, submitting several of the disease-specific tests included in its test kit.

A spokeswoman for the Mountain View, Calif.-based company said 23andMe recognizes it has been late responding to FDA questions about the application.

The FDA letter suggests that regulators have gone to great lengths to try and work with the company, citing months of meetings and dozens of letters between the two parties.

“However, even after these many interactions with 23andMe, we still do not have any assurance that the firm has analytically or clinically validated” its technology, states the letter.

The FDA warning takes issue with a number of claims the company makes for its test kit, particularly calling it a “first step in prevention” against diseases like diabetes, heart disease and breast cancer. Regulators worry that false results from the test could cause patients to receive inadequate or inappropriate medical care. For instance, 23andMe says its test can identify women who carry the BRCA gene mutation that significantly increases the risk of breast and ovarian cancer. But a false result could lead women to undergo unnecessary screening, chemotherapy and surgery.

The FDA gives the company 15 days to respond in writing to the letter’s concerns. Warning letters are not legally binding, but the government can take companies to court if they are ignored.

23andMe executives previously said that they first contacted the FDA in 2007, before launching their product. The agency did not take an interest in the technology until 2010, when it issued letters to several testing companies, warning that their products must be approved as safe and effective.

The FDA already regulates a variety of genetic tests administered by health care providers. The FDA’s concern with 23andMe appears to center on its marketing approach, which sidesteps doctors and health professionals.

Consumers order the company’s $99 product online. Once the kit arrives by mail they are instructed to spit into a small tube, providing a saliva sample which is sent back to the company for analysis. 23andMe says the customer’s DNA is analyzed to determine their likelihood of developing various diseases and responding to various drugs. The test also claims to provide information about ancestral background, though this information is not regulated by the FDA.