Shares of drugmaker Biohaven (BHVN.N) fell 19.6% to $12.1 in premarket trading.
The company's BHV-7000 program was partially placed on clinical hold after the FDA sought more information about a potential safety issue seen in animal studies.
The pause affects only new patient enrollment, while more than 600 patients already enrolled in the study can continue receiving treatment, the company said.
BHV7000-303 remains on track to report topline data in the second half of 2026.
If losses hold, BHVN is set to open at its lowest level since mid-June.
Twelve of 17 brokerages rate the stock "buy" or higher, four "hold" and one "sell"; their median price target is $20, according to data compiled by LSEG.
As of the last close, BHVN stock was up 32.9% year to date.
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