As Sanofi-Aventis picks itself off the floor after the beating it got from an advisory panel in the USA over the obesity drug Acomplia, analysts have been assessing the effect that non-approval across the Atlantic will have on the firm.

Shareholders in Europe reacted badly to the news that the US Food and Drug Administration's Endocrinologic and Metabolic Drugs Advisory Committee voted 14-0 against approving Acomplia (rimonabant), saying that the benefits do not outweigh the risk of psychiatric adverse effects seen in patients taking the drug, including suicide and seizures. Their disappointment led to Sanofi’s shares ending the day down 6.3% at 63 euros, their steepest fall since April 2004.

Acomplia is now going up in front of the European Medicines Agency next week regarding ongoing safety monitoring of the drug which was approved in Europe in June last year. The EMEA will obviously look at the FDA panel’s decision to see whether any further action is necessary, even though Acomplia’s label already carries a warning about psychiatric side effects. Suspension of the drug is highly unlikely, said analysts at Morgan Stanley who said "we see the potential for some label tightening in Europe, but a low probability of withdrawal".

Sanofi’s hopes that rimonabant would be a blockbuster have been dashed somewhat and if any US approval of the drug, which would be called Zimulti there, does take place, it is “unlikely until the next decade at the earliest," said Bear Stearns analyst Alexandra Hauber in a research note.

In another note, Paul Diggle of Nomura Code said that "if we assume the drug stays on the market outside the USA with a tougher label or is approved as a secondary product, sales won't be the $3 billion to $5 billion some people expected." He added that Zimulti was the most important product in Sanofi’s pipeline, which has "relatively few growth drivers."

JP Morgan downgraded the stock from ‘overweight’ to ‘neutral’, while reducing their estimates from 78 to 65 euros, noting that Sanofi is also facing the risk of generic competition for its anticoagulant Lovenox (enoxaparin), and the rumours that Total and L’Oreal are expected to dispose of their stakes in the Franco-German drugmaker will exert even more pressure on the company’s share price.

Sanofi’s current plight has seen speculation grow that the firm may tread down the merger road and try to tie up again with Bristol-Myers Squibb. The company has underperformed its European peers by some 15% over the last year, and it still has a patent dispute over the antithrombotic blockbuster Plavix (clopidogrel) preying on its mind so long-time partner B-MS, with its reasonably healthy pipeline is looking attractive again.