An Ayahuasca ceremony involves drinking the Ayahuasca brew, commonly a group activity (which can also be one-on-one, by the way) that is usually led by a Shaman, Curandero, or Ayahuasquero, and which typically starts in the evening or night, and ends when the effects of the brew wear off. The effects of the drink lasts for many hours and can span the entire night.
Throughout retreats, and depending on the duration of a retreat (a few days or weeks, etc.), one will generally participate in several Ayahuasca ceremonies. Nevertheless, one is never obliged to actually drink the brew if one doesn’t feel like doing so.
Often there are first a range of preparations before the actual drinking of Ayahuasca, which can include cleaning of the space where the ceremony is held, performing the Mapacho ritual, saying prayers and blessings, carrying out protective rituals, chanting, and singing of Icaros.
Mind that the content, form, and style of Ayahuasca ceremonies differ depending on the background and lineage of the retreat organizer, Shaman, or Curandero. Additionally, the effects of each Ayahuasca session are different for individual participants, and different each time Ayahuasca is drunk.
In any case, often the ceremony itself begins in silence, and each participant goes to take a cup of Ayahuasca given by the Shaman or retreat leader. The Shaman may speak briefly to each participant about intentions, personal issues, and may give some specific recommendations.
The Shaman often drinks a cup as well, usually after everyone has received a cup. The ceremony continues with dimmed or extinguished lights, the effects of the brew kick-in, and the Shaman may start to sing Icaros.
The Shaman then may engage in individual healings or support of the participants, as needed. Healing may involve singing specific Icaros for individual participants, removing negative energies by smoking and blowing Mapacho Tobacco, sprinkling holy water, and exercising Breathwork, among other things.
Sometimes, the group or individual participants may have another cup of the brew, if advisable or needed, or if the ceremony was set up to supply several smaller doses during its course.
Typically, the ceremony will end when the effects have clearly worn off or when dawn breaks through. The ceremony closing will be carried out more or less officially with blessings, prayers, advice, singing of Icaros, and maybe a general discussion to share experiences within the group or with the Shaman.