Safety and Efficacy of FSD201 for the Treatment of Chronic Pain Associated With Idiopathic MCAS (MCAD)

Key Inclusion Criteria: * Clinical diagnosis of idiopathic MCAS as per the global consensus diagnostic criteria * Adults with widespread chronic pain (in three or more body regions); * Chronic pains of intensity greater than or equal to 4.0 but less than or equal to 9.0 on a Numeric Pain Rating Scale, symptom duration of more than 6 months; * Subject agrees to use only acetaminophen (up to 1000 mg per dose and not to exceed 3000 mg/day) or diphenhydramine (up to 300 mg/day) as rescue medication for chronic widespread musculoskeletal nociplastic pains throughout the trial; * The subject is willing to maintain current activity and exercise levels throughout the study; * During the study, the subject agrees not to initiate or change any non-pharmacologic interventions (including chiropractic care, physical therapy, psychotherapy, and massage therapy). Any ongoing non-pharmacologic intervention must be stable for at least 4 weeks before screening and should be continued for the duration of the study; Key Exclusion Criteria: * The subject has pain that cannot be clearly differentiated from or that could interfere with the assessment of chronic musculoskeletal nociplastic pain secondary likely to idiopathic MCAS (post-herpetic neuralgia, traumatic injury, prior surgery, complex regional pain syndrome); * Adults with chronic cancer pain; * Adults with inflammatory connective tissue disorder or rheumatological disorder-related pain, for example rheumatoid arthritis; * Adults with focal musculoskeletal pain; * Adults with skin diseases (chronic urticaria, pemphigus, lupus, rosacea etc.); * Adults with endocrinological disorders (acute hypothyroidism, acute adrenal insufficiency etc.); * Adults with systemic gastrointestinal conditions (Inflammatory bowel disorders); * Significant psychological comorbidities: PHQ-9 score greater than 20; and GAD-7 score greater than 15 (indication of severe anxiety that could interfere with accurate logging of pain ratings); * Current or recent (within 12 months of screening) history of a substance use disorder including cannabinoid or alcohol use disorder as defined by the Diagnostic and Statistical Manual of Mental Disorders (5th edition; DSM-5); * Subject has neurologic disorder unrelated to chronic widespread musculoskeletal nociplastic pains (phantom limb from amputation, vitamin B12 deficiency, chronic inflammatory demyelinating polyneuropathy), circulatory disorder (peripheral artery disease), a skin condition in the area of …