Treatment of Persisting Symptoms After Concussion With Psilocybin Assisted Therapy

The goal of this randomized controlled trial is to evaluate the safety, feasibility, and efficacy of psilocybin assisted therapy as an intervention to reduce symptom burden in adult patients (aged 18-65) with persisting symptoms after concussion (PSaC). This trail will test the following 2 aims: AIM 1 : To test the safety and feasibility of an active psilocybin-assisted psychotherapy to an active control for patients with PSaC. AIM 2: To evaluate the efficacy of an active psilocybin-assisted psychotherapy compared to an active control as a treatment for PSaC. Participants will be asked to: * Complete a 2-part screening process * Attend a baseline assessment * Complete a psychoeducation preparation session(s) * Attend psilocybin administration session (receive high dose \[25mg\] or low dose psilocybin \[1mg\]) * Complete 5 weekly sessions of Acceptance and commitment therapy (ACT) * Repeat outcome measures at 1-week, 4 weeks, 3 months, and 6 months post-psilocybin administration (online only at 6 months).