A Swedish Internet CBT for Prolonged Grief Disorder: a Three-armed RCT

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