Prolonged Grief Disorder

The primary purpose of this study is to explore the feasibility of conducting a clinical trial on the effects of psilocybin for individuals with prolonged grief disorder (PGD).

The goal of this clinical trial is to pilot the effectiveness of an 8-week standardized Mindfulness Training program to decrease the psychiatric and somatic symptoms of prolonged grief disorder (PGD) and to examine changes in physiological and neuroimaging biomarkers of bereavement-related stress reactivity that are associated with Mindfulness Training in grieving adult patients (men and women, aged 18-60) who are diagnosed with PGD. The main questions it aims to answer are: 1. What is the effectiveness of Mindfulness Training to lower PGD symptom severity? 2. What is the effectiveness of Mindfulness Training on physiological and neuroimaging biomarkers of stress reactivity? 3. What are the potential mechanisms of treatment change of Mindfulness Training? Participants will be: * randomly assigned to immediately receiving an 8-week Mindfulness Training program or after a 12-week waitlist. * assessed for psychiatric and somatic symptoms and for physiological responses during a baseline, midpoint and endpoint visit, and at a one-month follow-up visit. * assessed for functional neuroimaging biomarkers of bereavement-related and general stress reactivity at the baseline and endpoint visits using a script-driven imagery task (which induces bereavement-related stress reactivity during an imagery of a personal situation related to the death compared to imagery of a neutral personal situation), and loud tones stress task (which induces general stress reactivity). Researchers will compare the Mindfulness Training group (which consists of patients with PGD who will receive the Mindfulness Training immediately) with the waitlist control group (which consists of patients with PGD who are waiting on a waitlist to receive the training after the Mindfulness Training group) to investigate if they differ in PGD symptom severity as well as physiological and neuroimaging biomarkers of stress reactivity.

Grief is a normal response after the death of a loved one. With time, the grief response decreases and people learn to cope with their loss. However, for some, the response becomes more intense and distressing. This is called prolonged grief disorder (PGD). People with PGD experience emotional pain and a deep longing for their loved one. PGD normally occurs \<10% of people after a loss, but it has become more common since the COVID-19 pandemic (\~30%). If left untreated, PGD leads to poor quality of life and increased risk of death. Treatment options such as medication and therapy are available; however, they can cause negative side effects and take a long time to work. To help individuals with PGD, we need treatments that work well and quickly. Repetitive transcranial magnetic stimulation (rTMS) is a safe, non-invasive treatment that delivers magnetic pulses to brain areas responsible for mood. rTMS has been approved in Canada to treat mood disorders. There is research to show that rTMS is safe and well-tolerated, and that works well in treating Post-Traumatic Stress Disorder (PTSD), a condition with similar symptoms to PGD. To determine whether rTMS is effective for treating PGD, we first need to determine if rTMS as a treatment for PGD is safe and feasible among grieving individuals.

The goal of this clinical trial is to evaluate the effectiveness of internet-delivered Cognitive Behavioral Therapy (iCBT) in reducing symptoms of prolonged grief in adults diagnosed with prolonged grief disorder. The main questions the study aims to answer are: * Does iCBT reduce symptoms of prolonged grief disorder, posttraumatic stress, and depression following the death of a loved one in the short and long term? * What mechanisms contribute to the effectiveness of iCBT in treating prolonged grief disorder? The iCBT intervention will be compared to a waitlist control group and an active control group to see if iCBT reduces symptoms of prolonged grief disorder more effectively than no treatment or a placebo treatment. Participants will: * Be randomly assigned to either the iCBT group, an active control group or a waitlist control group * Complete online assessments of symptom severity, grief cognitions, and level of avoidance before, during and after intervention * Engage in 10 weeks of a therapist-guided online treatment