How to describe the effects of magic mushrooms, or psychedelics in general. ?

Go read Fear and Loathing in Las Vegas by Hunter S. Thompson for a start. He was often loaded on drugs and that book alone is one hell of a trip.

Writers research and Yahoo isn't it. If you want to describe this accurately start with reading books where a character (or characters) get sh*tfaced on drugs.

ETA:

@Anon: People have never experienced aliens invading, ghosts are questionable, flying cars don't exist, hobbits don't exist, gnomes and fairies don't exist. Yet people still write them into stories all the time. It helps to know or experience what you're writing about, but when it comes to fiction an imagination is just as important. Most writers have never committed a murder or kidnapped a person and yet there are many novels about it. Don't rely too heavily on the "Write what you know" advice. It's useful, but it doesn't always apply.

Send an email to the eejit that asked the question, below, and ask them. They sound as if they wrote it whilst in the "drooling imbecile" stage of a nice, 60-dose of liberty-cappage. Believe me I know.

There are plenty of sources, ranging from general-audience books to very technical scholarly medical journal articles, that contain the information you're looking for. There's no need to desperately beg for descriptions on a forum filled mostly with 13-year-old illiterates and computerized Russian trolls. 

Most authors reach a point while writing a book when they need to hit the library and do some grown-up research. This is that point for you.

Rule #1 about writing: never try to write about anything you do not know or have not experienced. You'll be immediately spotted as a fraud. Change your story.