It works by taking money from you and giving it to the snake oil salesmen. The side effects are a poorer, but wiser you.
References :

No, I haven’t used it, and I would only use it if I was absolutely sure it was free of bacteria. The Wall Street Journal tested competing products and found it contained E. coli. I’m no scientist, but I know E. coli won’t make my penis bigger.

Side effects may include "migraines, dizziness, insomnia, anxiety, and even mood swings," according to extenzetruth.com before it was bought out by the company that makes Extenze and turned into an ad for it.

As long as your penis can deliver sperm where it counts, don’t worry about its size.
References :
http://www.ehow.com/about_5114659_extenze-male-enhancement.html

http://www.la.bbb.org/Business-Report/Maximizer-Health-Products-13168142

Of course I never used or will use it:the side effects are an empty wallet and a sales guy smiling on his way to the bank to deposit your money.
Dude it does not do one thing:a hoax a scam a fraud.
Colors
References :
Biology degree