Inclusion Criteria:
* ≥ 18 years of age.
* Capable of providing written informed consent for participation into the study.
* Willingness to allow the study team to review past medical records.
* At least one current PTLD-defining symptom (widespread pain, fatigue, or neurocognitive dysfunction) following completion of standard, recommended antibiotic therapy for treatment of Lyme disease, and that appeared in the first two years following first evidence of Lyme disease.
* Medical record documentation of meeting the Centers for Disease Control (CDC) case definition for clear diagnosis and treatment of early or late Lyme disease while living in a Lyme-endemic area. In other words, a history of physician-documented single or disseminated erythema migrans rash, late Lyme arthritis, or late Lyme neuropathy, OR Medical record documentation of meeting the CDC case definition for probable early or late Lyme disease. In other words, a history of abrupt onset of flu-like symptoms with or without a misdiagnosed rash, and concurrent positive serology while living in a Lyme-endemic area.
* Received treatment with a recommended course of antibiotics.
* Be medically stable as determined by screening for medical problems via a personal interview, a medical questionnaire, a physical examination, an electrocardiogram (ECG), and routine medical blood and urinalysis laboratory tests.
* Concurrent pharmacotherapy with selective serotonin reuptake inhibitors (SSRI), serotonin and norepinephrine reuptake inhibitors (SNRI), and/or bupropion is allowed if the type and frequency of the therapy has been stable for at least two months prior to screening. Allowable bupropion doses for participants will be ≤300mg/day.
Exclusion Criteria:
* Meeting Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for moderate or severe substance use disorder (excluding tobacco) within the past 5 years.
* Currently taking antipsychotics, monoamine oxidase (MAO) inhibitors, or antidepressant medications other than SSRIs, SNRIs, or bupropion. Allowable bupropion doses for participants will be ≤300mg/day.
* Currently taking lithium or other primary centrally-acting serotonergic medications, whether over-the-counter or prescription (e.g., efavirenz, 5-hydroxytryptophan, St. John's wort).
* Cardiovascular conditions: angina, a clinically significant ECG abnormality (e.g. atrial fibrillation or corrected QT interval (QTc) \>450msec), transient ischaemic attack (TIA) in the last 6 months, stroke, artificial heart valves, or uncontrolled hypertension with resting blood pressure systolic \>139 or diastolic \>89, or heart rate \>90 bpm.
* Renal disease (creatinine clearance \< 40 ml/min using the Cockcroft-Gault equation).
* Current or past history of meeting DSM-5 criteria for Schizophrenia, Psychotic Disorder (unless substance-induced or due to a medical condition), or Bipolar I or II Disorder.
* Family (i.e., 1st degree relative) history of Schizophrenia, Psychotic Disorder (unless substance-induced or due to a medical condition), or Bipolar I Disorder.
* Past-year hallucinogen use
* Received the Lyme vaccine when it was available (1998-2002).
* Development of unexplained chronic pain, chronic fatigue syndrome, fibromyalgia, autoimmune disease, or unexplained neurologic symptoms before first evidence of Lyme disease.
* Cancer or malignancy in the past 2 years.
* Epilepsy with history of seizures.
* Insulin-dependent diabetes; if taking oral hypoglycemic agent, then no history of hypoglycemia.
* Current dementia or related disorders including but not limited to, Alzheimer's Disease, vascular dementia, Lewy body dementia, and frontotemporal disorders.
* Current or past major immunosuppressive illness or medications.
* Currently pregnant or nursing.
* Currently of childbearing potential and not using effective methods of contraception.
* Not fluent in English.
* High risk for suicidal ideation or behavior (i.e., individuals who report suicidal ideation with intent or behavior on the Columbia-Suicide Severity Rating Scale (C-SSRS) at screening, or individuals with a suicide attempt within the past 3 years).