Regeneron

(REGN) - Get Report

was falling apart in the premarket after saying its anti-obesity drug produced only "small" weight loss in a clinical trial.

The biotech company said that while the drug, Axokine, showed statistically significant results in all of its endpoints, "the overall magnitude of the weight loss was small." That language spooked investors and the shares were down $8.76, or 51%, to $8.55 on the Instinet premarket session.

According to Regeneron, the study found that a greater proportion of Axokine patients lost at least 5% of their body weight, compared with patients getting a placebo. They also had a greater average weight loss: about 6.2 pounds compared with 2.6 pounds for the placebo group.

But weight loss associated with the Regeneron drug was limited by the development of antibodies after about three months of treatment in many of the subjects.

Regeneron said it's still analyzing the data. After completing it, the company will discuss the data with regulators, then talk about its plans for further development.