US biotechnology company Tonix Pharmaceuticals Holding Corp. (NASDAQ: TNXP) announced on Monday that the US Food and Drug Administration has cleared its Investigational New Drug application for TNX-102 SL in adults with major depressive disorder.

The clearance allows Tonix to proceed with the potential pivotal Phase 2 HORIZON trial, a six-week, randomised, double-blind and placebo-controlled study enrolling about 360 adults across roughly 30 US sites.

Tonix expects to begin recruitment in mid-2026, evaluating TNX-102 SL 5.6 mg as a first-line monotherapy with the primary endpoint measured by change in Montgomery-Asberg Depression Rating Scale scores at Week 6.

TNX-102 SL, a sublingual tablet formulation of cyclobenzaprine hydrochloride, is intended to target sleep disruption associated with depression, and previous studies in fibromyalgia and post-traumatic stress disorder have shown signals of improved depressive symptoms. The therapy is also in development as a daily bedtime treatment for acute stress disorder under an Investigator-initiated IND.

Tonix noted that TNX-102 SL has been generally well tolerated in prior registrational studies, with a lower incidence of common antidepressant-related side effects.

Major depressive disorder affects more than 21 million adults in the United States each year and remains an area where many existing treatments offer limited relief or are discontinued due to tolerability issues.