June 4 (Reuters) - A panel of advisers to the U.S. Food

and Drug Administration will meet on Tuesday to discuss a

therapy based on the psychedelic drug MDMA for patients with

post-traumatic stress disorder (PTSD).

The meeting by the agency's independent experts is the

farthest that a drug based on MDMA, commonly known as ecstasy or

molly, has ever reached in the FDA regulatory process for

approval.

It follows a decades-long push by advocates who say drugs

like MDMA can treat mental health disorders and have therapeutic

applications beyond their illicit use.

The treatment is a capsule form of MDMA made by the

public-benefit corporation Lykos Therapeutics and is intended to

be administered along with sessions of talk therapy by a

licensed mental health provider.

In clinical trials in over 190 patients, those who received

doses of MDMA in addition to therapy showed a significant

reduction in PTSD scores compared to placebo.

However, the FDA's staff reviewers on Friday raised concerns

that patients in the trials were aware of whether they were

given MDMA or a placebo due to its psychedelic effects, clouding

how well the drug worked.

"I don't think that is as much of a concern because even if

it is an enhanced placebo effect, people are still getting

better," said David Olson, director of the UC Davis Institute

for Psychedelics and Neurotherapeutics.

"But the bigger question is what is the risk to those

individuals?"

PTSD affects 13 million Americans and is especially

common among war veterans. There remains a large unmet need for

new treatments for PTSD as existing drugs do not work on all

patients.

The Lykos treatment is one among several psychedelic drugs

being tested in patients with hard to treat mental health

conditions such as Compass Pathways' ( CMPS ) drug, which uses

the same component as magic mushrooms.

The FDA's staff proposed restrictions around its use and

monitoring in their briefing documents on Friday. The FDA also

flagged a rise in blood pressure and pulse in the trials and

cases of liver toxicity.

The approval could offer "a new avenue of treatment, but

itself is not going to make a big dent", due to costs and

complexities associated with it, said Olson.

"It's important because it would be the first in this class

of molecules, but I don't think it will be the last, it will be

replaced by compounds that have superior properties to MDMA."

(Reporting by Sriparna Roy and Pratik Jain in Bengaluru;

Editing by Arun Koyyur)