05:22 AM EST, 02/19/2025 (MT Newswires) -- Supernus Pharmaceuticals ( SUPN ) shares fell over 20% in Wednesday's premarket activity after the company said overnight its phase 2b study of SPN-820 in adults with treatment-resistant depression "did not" demonstrate a statistically significant improvement on the primary endpoint.

There was no treatment difference between SPN-820 and placebo in the change from baseline to week 4 for the secondary endpoints, the company said late Tuesday.

The multi-center, double-blind trial examined the efficacy and safety of SPN-820 over four weeks of treatment and then a week of "blinded placebo-washout" in about 250 patients from roughly 40 clinical sites.

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