UPDATE 3-Forest Labs, Pierre Fabre drug fails to meet goal

* Drug fails to meet statistical significance

* Two more late-stage studies planned

* Drug was well tolerated

* Forest shares slip in early trading (Adds analyst comment, updates share movement)

CHICAGO, Jan 20 (Reuters) - Forest Laboratories Inc (FRX.N) and Pierre Fabre Medicament said preliminary results from a Phase III study of levomilnacipran to treat Major Depressive Disorder failed to meet its goals.

Forest's shares slipped about 6 cents to $31.84 in early New York Stock Exchange trading.

Study results were based on the psychiatrist-rated diagnostic questionnaire known as the Montgomery-Asberg Depression Rating Scale. Differences between those in the drug group and those in the placebo group were not great enough to be considered statistically significant, the companies said on Thursday.

Eighty percent of patients, from 18 to 80 years old, completed the study. Eight percent dropped out because of the negative side effects, compared with 2 percent in the placebo group. The most common adverse side effects were nausea and headache.

The companies said the study was part of the ongoing development program for levomilnacipran. The two additional placebo-controlled Phase III studies of the drug in patients with Major Depressive Disorder are currently under way.

Results from those studies are expected to be available in the second half of the year.

Aaron Gal, an analyst with Bernstein Research, said he was confident the drug would eventually prove to be effective. He noted that levomilnacipran is in a class of drugs known as selective serotonin reuptake inhibitors, or SSRIs.

"The efficacy of SSRI is relatively low versus other drug classes and thus if something goes wrong in the patient pool, the primary end point could be missed. This is part of the reason companies sometimes do three pivotal trials when only two are needed," he wrote in a research note.

We are confident the active ingredient is active," he said.

Gal said the drug was not a substantial factor in valuing Forest shares. (Reporting by Debra Sherman, editing by Lisa Von Ahn and Maureen Bavdek)