Could a common blood pressure pill ease PTSD nightmares in veterans?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * ≥18 years old * US military veteran * Currently has PTSD diagnosis as determined by clinical diagnosing or by the PI * Screening score on PCL5 minimum of 40 (per data from previous studies36-38, a PCL5 score of 40 is roughly equivalent to a CAPS score of 30) * Scores ≥10 on PCL5 items 1-5 (intrusion) or scores ≥10 on PCL5 items 15-20 * From PCL5 questionnaire, must score the following minimum in each of the following categories: * 1x score of 2 on Questions 1-5 * 1x score of 2 on Questions 6-7 * 2x score of 2 on Questions 8-14 * 2x score of 2 on Questions 15-20 * Has score ≥3 on CAPS nightmare items B2 and E6 * Speaks and understands English * Willing to come into the clinic as programmed Exclusion Criteria: * Pregnant or breastfeeding * At Moderate or High risk of suicide based on "past month" column of the Columbia-Suicide Severity Rating Scale (CSSR-S) screen version - recent. * Has acute or unstable mental illness or any cognitive issues which the PI determines would interfere with engagement in the study (e.g., active schizophrenia, uncontrolled bipolar, history of neurocognitive impairment, history of moderate-severe traumatic brain injury) * Currently receiving exposure therapy * Recently enrolled (\<1 month) in other behavioral health therapies (exclusions made at the PI's discretion depending on therapy type and length since admission) * Urgent hypertension (BP above 160/100) or symptomatic of hypertension (having a hypertensive emergency) * Blood pressure under 100/60 or symptoms of low blood pressure (light headedness, dizziness, heart palpitations, or other symptoms as determined by clinician). * Any contraindications to taking clonidine such as: * Known hypersensitivity to clonidine * History of 2nd or 3rd degree atrioventricular block * History of sinus bradycardia * History of pheochromocytoma * History of Raynaud's phenomenon * Stage 5 Kidney disease * Recent myocardial infarction (\<6 months) * History of cerebrovascular disease or recent stoke (\<6 months) * Have used any of the following drugs in the past 30 days, unprescribed or not used as prescribed: * Heroin * Other opiates/analgesics * Barbiturates * Other sedatives/, hypnotics, or tranquilizers * Cocaine * Amphetamines * Cannabis * Hallucinogens * Inhalants * Currently have any of the following diagnoses: * Opioid use disorder * Cocaine use disorder * Alcohol use disorder * Cannabis use disorder * Sleep apnea diagnosis with verbal indication of non-adherence to treatment * Were prescribed clonidine within the last 6 months * Any α2 agonist * Catapres/Kapvay (clonidine) * Aldomet (Methyldopa) * Zanaflex (Tizanidine) * Intuniv (Guanfacine) * Lucemyra (Lofexidine) * Any α1-adrenergic antagonist * Prazosin * Terazosin * Doxazosin * Silodosin * Alfuzosin * Tamsulosin * Any opiate (e.g., buprenorphine, hydrocodone, oxycodone) * Any antipsychotic medication * Haldol (haloperidol) * Loxitane (loxapine) * Mellaril (thioridazine) * Moban (molindone) * Navane (thiothixene) * Prolixin (fluphenazine) * Serentil (mesoridazine) * Stelazine (trifluoperazine) * Trilafon (perphenazine) * Thorazine (chlorpromazine) * Abilify (aripiprazole) * Clozaril (clozapine) * Geodon (ziprasidone) * Risperdal (risperidone) * Seroquel (quetiapine) * Zyprexa (olanzapine) * Benzodiazepines * Cyproheptadine * Based on PI or study team assessment is cognitively unable to engage in the study * Has a legal guardian