Investigation of Sulindac (HLX-0201) and Gaboxadol (HLX-0206) in Male Fragile X Syndrome Patients Aged 13-40

Inclusion Criteria: * Subject consents to participate, or if the subject are not the subjects own legal guardian, offers assent supported by legally authorized representative consent. Caregiver also commits to the study requirements prior to any study-related procedures * Willing and able to comply with the study procedures as specified in the protocol and to comply with the study drug administration * Subject and caregiver are both able to understand the spoken national language clearly and caregiver can read and write to complete study assessments * Males aged 13 to 40 years (inclusive) * Has FXS with molecular genetic confirmation of the full FMR1 mutation (\>200 CGG repeats). May have been confirmed historically or at Screening * Weight ≥45 kg * CGI-S score ≥4 * Is in general good health as deemed by the Investigator, determined by physical examination, medical history and laboratory tests * If receiving sertraline, is on a stable, well-tolerated dose for the previous 3 months with no further changes anticipated * Agrees not to discuss treatment outcomes on social media until subject has completed their End of Therapy visit Exclusion Criteria: * Active or history of peptic or gastric ulcer or hemorrhage * Any chronic major medical comorbid condition deemed by the Investigator as presenting added risk to the subject, including but not limited to refractory hypertension, kidney disease, or liver disease * Diagnosed with diabetes (Type 1 or II) or receiving any anti-diabetic medication * Unstable seizure disorder defined by any seizure within 6 months prior to baseline visit and/or a change in any anti-convulsant drug dosing in the 60 days prior to study entry * Patients with cardiovascular disease risk factors: Uncontrolled high blood pressure (systolic blood pressure \>150 mmHg), Unstable angina, History of documented myocardial infarction or cerebrovascular accident, NYHA Class III and IV heart failure, Known uncontrolled hyperlipidemia as LDL-C ≥190 mg/dL or triglycerides ≥ 500 mg/dL * Chronic use of NSAIDs or other anti-inflammatory agents * Currently taking or have taken any cannabidiol (CBD) preparation within 30 days prior to screening * Currently taking or have taken sulindac or gaboxadol within 30 days prior to screening * Currently taking GABAergic agents (i.e., acamprosate, baclofen, vigabatrin, tiagabine, riluzole, benzodiazepines, and gabapentin) * Changes in psychotropic or anti-convulsant (where taken for reasons other than seizure control) drug treatment within 30 days prior to Screening * Significant changes in any educational, behavioral and/or dietary interventions the month prior to Screening * Planned initiation of new, or modification of ongoing, interventions during the study * History of adverse effects of sulindac or other NSAIDs that would prevent safe study completion * Unable or unwilling to take oral medication (whole capsule) or history of dysphagia or malabsorption * Has abnormal baseline laboratory assessments including, but not limited to, ALT or AST or total bilirubin \>1.5 × ULN, or other clinically relevant laboratory abnormality * Has a clinically significant abnormal ECG, heart rate or BP at Screening as judged by the Investigator * Has received an investigational drug (either approved or not approved) in any prior clinical study within 30 days or 5 half-lives (whichever is longer) prior to Screening