Drugmaker Lykos Therapeutics said the FDA notified the company that its drug “could not be approved based on data submitted to date,” and requested an additional late-stage study. Such studies generally takes several years and millions of dollars to conduct. The company said it plans to ask the agency to reconsider.

Lykos and other psychedelic companies had hoped that MDMA would be approved and pave the way for other hallucinogenic drugs to enter the medical mainstream. If the FDA had granted the request, MDMA, also known as ecstasy or molly, would have become the first illegal psychedelic to become a federally approved medicine.

The FDA’s decision was expected after a panel of government advisors voted overwhelmingly against the drug’s use for post-traumatic stress disorder in June. The negative vote came after an all-day meeting in which experts scrutinized Lykos’ study data, research methods and possible risks of the drug, including heart problems, injury and abuse.

FDA said Friday the MDMA application had “significant limitations” that “prevent the agency from concluding that the drug is safe and effective for the proposed indication.” The agency said it will continue encouraging “innovation for psychedelic treatments and other therapies to address these medical needs.”

Lykos said the issues FDA raised in what’s called a complete response letter echoed the concerns during the June meeting.

“The FDA request for another study is deeply disappointing,” Lykos CEO Amy Emerson said Friday in a statement. “Our heart breaks for the millions of military veterans, first responders, victims of sexual and domestic abuse and countless others suffering from PTSD who may now face more years without access to new treatment options.”

Lykos is essentially a corporate spinoff of the nation’s leading psychedelic advocacy group, the Multidisciplinary Association for Psychedelic Studies, or MAPS, which funded the initial studies of MDMA by raising millions of dollars from wealthy backers.

The group has been a pioneer in researching the medical use of psychedelics, which major pharmaceutical companies have been unwilling to fund. Two small studies submitted to the FDA suggested combining MDMA with talk therapy led to significant easing of PTSD symptoms.

Antidepressants are now the only FDA-approved drugs for PTSD, which is closely linked to depression, anxiety and suicidal thinking and is more prevalent among women and veterans.

In recent years, MDMA research has been widely publicized by combat veterans, who say the lack of treatments options for the condition has contributed to higher rates of suicide among military personnel. Last month, veterans supporting psychedelic therapy rallied on Capitol Hill in support of the drug. And more than 80 House and Senate lawmakers have signed letters to the FDA in recent weeks urging MDMA’s approval.

But FDA’s review brought new scrutiny to the research. The vast majority of patients in Lykos’ studies correctly guessed whether they had received MDMA or a dummy pill, making it “nearly impossible” to maintain the “blinding” which is considered essential for medical research, according to FDA internal staffers.

In recent months, separate allegations of misconduct have emerged, including that some researchers involved in the studies coached patients to suppress negative results or inflate positive ones.

Despite the setback, many experts say other psychedelics may fare better before the agency.

MDMA is the first in a series of psychedelics that are expected to be reviewed by the FDA in coming years as part of a resurgence of interesting into their therapeutic potential.

The idea of using psychedelics to enhance psychotherapy is not new. A handful of therapists in California used MDMA during the 1970s and 1980s — when it was still legal — to facilitate couples therapy sessions. MAPS was founded in 1986 to oppose a federal decision placing MDMA in the same ultra-restrictive drug category as heroin, LSD and other illegal psychedelics.

MAPS’ studies of MDMA began more than a decade ago. Since then, dozens of small, startup drugmakers have entered the field, studying other substances like psilocybin and LSD for conditions including depression, addiction and anxiety. Those studies are generally larger and more rigorous than the MDMA studies submitted to the FDA.

Two drug developers, Compass Pathways and Usona Institute, are conducting late-stage studies of psilocybin — the active ingredient in magic mushrooms — for severe depression.