The aim of this study is to compare the effectiveness of an ayahuasca-assisted constructivist therapy with constructivist therapy and no treatment to decrease the severity of grief. A secondary purpose is to assess the effectiveness to prevent Persistent Complex Bereavement Disorder and Prolonged Grief Disorder, and to assess potential changes in avoidance, meaning-making and self-clarity. Subjective effects and Acceptance promoting effects of psychedelic drug are assessed after ayahuasca administration. A non-randomized controlled trial is proposed with three arms involving an experimental group (ayahuasca in concert with psychotherapy) and two control groups (psychotherapy and no treatment) with pretest, posttest and 3 months follow-up.

Grief is a deep and intense sorrow caused by the loss of someone loved. Although every person could benefit from support, only a substantial minority of bereaved people experience severe, persistent and disabling grief (PCBD), requiring treatment one year after the death of a loved one. However, pharmacotherapy alone has not proven to be effective, and while psychological interventions for prolonged grief disorder may be efficacious, the clinical effectiveness is small (Hedges' g: 0.41-0.45). As far as we know, no bereavement prevention program has proven to be effective, and early interventions are discouraged. Thus, there are no effective resources for supporting the bereaved during the months following the death of a loved one, a need which peaks during the months following the death, when grief is most intense and the bereaved lives are at their highest level of risk.

Inclusion Criteria:

• Experienced the loss of a first- degree relative not more than 12 months prior to enrollment as indicated by self-report.
• Scores up to 40 in the Texas Revised Inventory of Grief (TRIG).

Exclusion Criteria:

• Pregnant or breastfeeding women.
• Hypertension (systolic blood pressure above 140 mm, diastolic above 90 mm and heart rate above 100 bpm).
• History of psychotic disorder (Axis I-II of the DSM-V).
• Substance use disorder (except nicotine).
• Alcohol consumption greater than 40 g/day.
• Receiving psychological or self-help therapy during the study on a regular basis.
• Receiving regular pharmacological therapy for complicated grief during the study.
• Regular intake of any type of medication in the month preceding the study.
• Treatment with single doses of symptomatic medication during the study may be accepted (as long as it can be assumed that the ingested drug has been completely eliminated on the days of the ayahuasca administrations).