Inclusion Criteria (Summary):  Ability and willingness to provide written informed consent and to comply with the study procedures. Fluency in the language of the investigator, study staff and the informed consent. Age 18-75 years. Diagnosis of primary (classical or idiopathic (with or without paroxysms)) trigeminal neuralgia as per the ICHD3 criteria confirmed by the study neurologist. Experience pain defined as at least three paroxysms per day, each rated at an intensity of 4 or more on a pain intensity numerical rating scale (PI-NRS) on at least four days per week. Pain should be present at least 2 months prior to study entry with or without continuous pain. Female patients who are either sterile or menopausal. For female patients with childbearing potential, must be neither pregnant nor lactating (with appropriate contraceptive precautions and prior negative pregnancy tests).  Exclusion Criteria (Summary):  Patients who meet any of the following criteria will be excluded from participation in this study:  Current or prior history of any major psychiatric diagnoses unrelated to TN. Patients with TN-related depressive symptoms are permitted. Current or prior history of mania, or psychotic episodes. History of DSM-5-defined substance dependence (Diagnostic and Statistical Manual for Mental Disorders, 5th edition) and/or substance abuse in the last six months [180 days], except for nicotine. Patient not willing to discontinue their current analgesics. Of note, gabapentin or pregabalin will be discontinued during the first 2 weeks in Period 1 at the latest. Use of opioids, except for pain control on a prn basis as long as it does not exceed 2 days per week. Known allergic reaction to the investigational drug or one of its components. Previous treatment with basimglurant. Treatment with antipsychotics within six months (180 days) prior to screening. Treatment of depressive symptoms with selective serotonin reuptake inhibitors is permitted if started more than 6 weeks prior to screening. However, use of low dose antipsychotics for reasons other than psychotic or bipolar disorders e.g., persistent insomnia, is allowed.  Any investigational drug within 90 days prior to initiation of study drug.  Medical status:  Evidence of clinically significant, uncontrolled, unstable medical conditions or recently diagnosed cardiovascular disease, such as ischemic heart disease, coronary artery vasospasm, and cerebral ischemia. Subjects with myocardial infarction, acute coronary syndrome, percutaneous coronary intervention, cardiac surgery, stroke or transient ischemic attack during the 6 months prior to screening. Subject has a history of gastric, or small intestinal surgery (including gastric bypass, gastric banding, gastric sleeve, gastric balloon, etc.), or has a disease that causes malabsorption. Body mass index > 33kg/m² Patients with moderate or severe impaired hepatic function, i.e., Pugh-Child score B or C. Patients with severe renal impairment, i.e., eGFR or creatinine clearance lower than 30mL/min.