Your question is not why celebrities do drugs, but why artists, musicians, and writers often have kindness for marijuana. The answer is marijuana really does help with creativity.
...[T]here’s some intriguing evidence that marijuana can actually
improve performance on some mental tests. A recent paper by scientists at University College, London looked at a phenomenon called
semantic priming. This occurs when the activation of one word allows us to react more quickly to related words. For instance, the word “dog” might lead to decreased reaction times for “cat,” “pet” and “Lassie,” but won’t alter how quickly we react to “chair.”
Interestingly, the scientists found that marijuana seems to induce a state of
hyper-priming, in which the reach of semantic priming extends to distantly related concepts. As a result, we hear “dog” and think of nouns that, in more sober circumstances, would seem rather disconnected, such as “leash” or “hair.” This state of hyper-priming helps explain why cannabis has been so often used as a creative fuel, as it seems to make the brain better at detecting those remote associations that lead to radically new ideas.
Why does marijuana increase access to far reaching intellectual connections? One possibility is that the beneficial effect of the drug is mediated by mood. Marijuana, after all, has long been used to quiet anxious nerves — big pharma is currently exploring targeted versions of THC as a next generation anxiolytic — as only a few puffs seem to dramatically increase feelings of relaxation and euphoria. (The technical term for this, of course, is getting stoned.) Furthermore, recent research has suggested that performance on various tests of remote associations and divergent thinking — a hallmark of creativity — are dramatically enhanced by such positive moods. Look, for instance, at a 2003 study by German researchers that investigated performance on a classic remote associate test (RAT), in which subjects have to find a fourth word that is associated with the three following words:
cottage Swiss cake
This answer is pretty obvious: cheese. But what about this problem?
dream ball book
That was a trick question: There is no shared association. Here’s the remarkable thing about these remote associate problems: People can recognize the possibility of a solution before they’ve solved the problem. The German scientists demonstrated this by asking people to quickly press the spacebar whenever they were presented with a triad that had an answer. If people had no intuitions about creative associations, their guesses should have been roughly random. But that’s not what the scientists found. Instead, subjects were able to efficiently sort “coherent” word problems — those with an actual answer — from incoherent problems, which are a waste of time. Before we find the solution, we can feel its presence.
And this returns us to marijuana: Putting people in a positive mood roughly doubled their accuracy at the task. All of a sudden, they were twice as good at identifying problems with possible solutions. This suggests that anything that makes us happier, reducing vigilance and anxiety, might also make us more creative. We can detect more remote associations, of course, but we also know which associations are worth pursuing, which is probably even more important. It doesn’t matter if it’s pot, chocolate or a stand-up comic — those substances or experiences that put a smile on our face can also increase the powers of the imagination, at least when solving particular creative problems.
http://www.wired.com/wiredscience/2011/08/does-marijuana-make-you-stupid/
Creativity is a numbers game. It's trial & error of sifting through different combinations of patterns, going through thousands of bad ideas until you find the one great gem of an idea in the sand. When an artist is painting or sketching, countless options are evaluated in-between every stroke.
