UPDATE 1-Solvay ends research on obesity drug

(adds details, background throughout, changes dateline, pvs Brussels)

LONDON, Nov 17 (Reuters) - Belgian drugs, chemicals and plastics maker Solvay (SOLB.BR) said on Monday it was ending its research into an experimental obesity drug.

The compound known as ibipinabant was in phase II development and is the latest in a once-promising class of drugs for obesity to be shelved.

Earlier in November, Sanofi-Aventis (SASY.PA) pulled the plug on Acomplia -- once its biggest new drug hope -- while Pfizer (PFE.N) announced on the same day it was terminating late-stage development of its experimental obesity drug otenabant.

Another so-called cannabinoid 1 (CB1) receptor antagonist in development is AZD-2207 from AstraZeneca (AZN.L), which is in in mid-stage Phase II tests, Thomson Pharma data showed.

Claus Steinborn, head of R&D at Solvay Pharmaceuticals, said the decision was not related to any adverse events or the efficacy of the compound.

"We have made this decision after careful evaluation of the current regulatory environment, leading to new and high regulatory hurdles for approval of a compound of this class," Steinborn said in a statement.

CB1 drugs work by blocking the same receptors in the brain that make people hungry after smoking marijuana. They have also been linked to psychiatric side effects, such as depression and suicidal thoughts.

Acomplia, which led the field, had already been withdrawn from the European market last month after being linked to mental disorders. It failed to win regulatory clearance in the United States in 2007.

Merck & Co (MRK.N) last month stopped development of its obesity drug in the class, taranabant, due to side effects at higher doses.

Evaluate Pharma, which compiles consensus drug forecasts, said the failure of the three most advanced CB1 medicines had effectively wiped out $14.4 billion in potential cumulative revenues 2007 and 2012, compared with analyst forecasts just 18 months ago.

Prior to the rejection of Acomplia in the United States in 2007, hopes for CB1 medicines had been riding high. However, the U.S. rebuff and an increasingly cautious climate among regulators worldwide caused analysts to cut bullish sales projections. (Reporting by Michael Kahn, additional reporting by Brussels bureau; Editing by Andrew Macdonald)