Are there long-term dangers to drinking ayahuasca?

There is a popular idea that repeated use of psychedelics over years will leave you 'fried', mentally impaired and out of touch with reality. Contrary to this, any long-term ayahuasca-drinkers I have met seem to have some indefinable human quality about them, a sort of glow and optimism. It's something that you are familiar with if you have hung around people who have done other mystical disciplines like yoga for many years.

I don't know what makes the difference between ayahuasca-drinkers and 'acid casualties'. It could be that ayahuaca is more benign, but seeing as no psychedelic can be linked to brain damage, it seems more likely that the benefits come from the supportive, ceremonial set-and-setting around ayahuasca-drinking.

A few scientific studies have investigated long-term effects of ayahuasca -

A 1999 study called 'Do hallucinogens cause residual neuropsychological toxicity?' concludes that "the literature tentatively suggests that there are few, if any, long-term neuropsychological deficits attributable to hallucinogen use."

A 2008 paper by the same author called 'Evidence of health and safety in American members of a religion who use a hallucinogenic sacrament' interviewed 32 ayahuasca drinkers. They had consumed ayahuasca between 20 and 1300 times and the researchers were not able to find any evidence of damage.

'Risk assessment of ritual use of oral dimethyltryptamine (DMT) and harmala alkaloids' is a systematic search of all the scientific literature about ayahuasca and DMT, especially looking at studies when animals were given these drugs over long periods of time. It was found that none of these studies found long-term damage.