A friend of me wants to try ayahuasca. He takes ritalin, so i told him that this could be a dangerous combination. I advised him to gradually reduce the ritalin intake to zero, prior to taking ayahuasca and to stay abstinent at least a few days.
I thought it's better just to be carefull.
Does anybody know anything about the ritalin MAOI combination and the possible dangers?

Perhaps this is not the best place to ask for medical advice of this nature. A quick google search brings up a couple of pages stating that combining methylphenidate + MAOI is not recommended due to a possible rise in blood pressure (but I don't know if this is reliable information, or whether the contraindication applies to both MAO-a and MAO-b inhibitors).

As an aside, I wonder if the ritalin withdrawal might negatively affect your friend's mental state during the ayahuasca experience.

Ayahuasca is a strong compound I would not in any way reccomend you let him try it. I know ritalin is used to treat A.D.D. which isnt really a hardcore mental disorder but the fact that he has been on it means his brain chemisrty isnt exactly perfect and exposing him to something like this could cause some serious trauma. It's not a 5 minute trip either so he cant just hang on until he comes down from it.

I think the combination of an MAOI and ritalin is nothing to worry about. I have seen people prescribed to both at the same time. But I wouldn't risk trusting some guy on the internets word.
If you have an iPod or windows mobile I would suggest downloading epocrates (http://www.epocrates.com/). It shows everything you need to know about perscription drugs, including pharmacology and interactions with other drugs.

Well, i recommended him not to take the risk. So if he really wants to go this way, he knows about the possible dangers. It's his responsability now to do some research or to consult his doctor about it, etc.
Better safe then sorry.