Ayahuasca can have extreme negative health effects if taken with some presciptions drugs, especially antidepressants such as Prozac and other selective serotonin reuptake inhibitors. A few deaths have been attributed to the use of ayahuacsa, although the causes of the deaths have not all been conclusively determined. In at least some cases ayahuasca use might have directly resulted in the fatality. The primary risks associated with ayahuasca are the inclusion of a MAOI as a definitional component of the brew and the fact that there is no single recipe for ayahuasca and admixture plants can include any of a wide variety of psychoactives including Datura or Brugmansia. MAOIs can be dangerous because they inhibit an enzyme important in the metabolic breakdown of many foods and drugs. The combination of MAOIs with certain drugs, particularly stimulants, can lead to dangerous or potentially fatal medical situations. Traditional ayahuasca use involves a complex set of pre-ceremony dietary guidelines that exclude many foods and modern shamans require that participants stop using most pharmaceuticals (even anti-malarial and anti-diarrhea drugs) in order to take ayahuasca with them. Additionally, the strength/potency of ayahuasca brews varies from batch to batch, which can impact the risks related to contraindicated combinations. Finally, the term "ayahuasca" is sometimes used for "pharmahuasca" or blends of pure or extracted chemicals combined to mimic the effects of the traditional ayahuasca brews. The health risks associated with all drugs are dose-dependent and pharmahuasca-type ayahuascas can easily include much higher dose levels than plant-based ayahuascas and are often consumed by less experienced self-experimenters and often without experienced sitter/guide.