A Study to Evaluate the Efficacy and Safety of TNX-1900 in Patients With Chronic Migraine

Major Inclusion Criteria: * Men and women aged 18 to 65 years, inclusive, at the time of Visit 1. * History of migraine with or without aura for at least 1 year and onset at \< 50 years of age. Patient must also have a history of chronic migraine \> 3 months prior to Visit 1 as defined by IHS ICHD-3 * Patients can be on stable ≤ 1 preventive medication and any number of abortive migraine medications for 90 days prior to Screening and during the study. All treatments, other than the study drug, thought to have preventive efficacy in migraine should not be started or discontinued during the entire study period. Note: Up to approximately 30% of the patients randomized into the study can be on 1 preventative medication. Once this category is filled, only patients who are not on any preventative medications can be randomized into the study. Major Exclusion Criteria: * History of cluster headache. * Presence of headaches more than 26 days a month on average for the 6 months prior to Screening. * Failed to benefit from an adequate dose and duration, in the investigator's judgment (eg, one month of β-blocker), of 3 or more migraine preventive medications. * Use of opiates or barbiturates more than 4 days per month for more than 3 consecutive months prior to Visit 1 and during the study. * Use of over-the-counter (OTC) nasal products (ie, saline spray, Neti-Pot, Naväge® etc.) during the study. * Any use of intranasal corticosteroid medications or conditions in which use of intranasal corticosteroids may be indicated during the study, eg, unstable allergic rhinitis that has previously required intranasal corticosteroids. Intranasal corticosteroid use is not allowed within 28 days of Baseline/Randomization/Visit 2 and during the treatment phase or follow-up period of the study. * Patients who recently discontinued treatment with an anti-calcitonin-gene-related peptide (CGRP) or participated in anti-CGRP clinical study must be at least 4 months from the last drug administration prior to Visit 1.