Allergan ( AGN) shares fell early Tuesday after a regulatory advisory panel expressed reservations about the company's oral psoriasis treatment Tazoral.

The Food and Drug Administration panel late Monday said Allergan should undertake more tests to address questions about the drug's potential to cause birth defects.

The Irvine, Calif.-based company said it was disappointed by the decision, but added it will continue to work with the FDA on the approval process.

The panel's conclusion is important because it is rare for the FDA to reject such recommendations.

Psoriasis is a painful skin condition.

Allergan shares fell $5.01, or 6.1%, to $76.90 in premarket action.

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