Hollywood actor Brad Pitt has denounced America's controversial war on drugs, branding it a failure and a charade.

The Fight Club star, who is an executive producer of new documentary The House I Live In, about U.S. officials' long-running battle to stamp out the drugs trade, has written a scathing essay about the way the issue has been handled.

In the article, published by Britain's The Observer, he insists illegal substances are still "laughably easy" to buy on the streets and suggests efforts to end the trade in illegal narcotics are a waste of money.

Pitt writes, "Today, with very little effort, anyone can land in virtually any city in this country, and within a day or two, procure their drug of choice. Since declaring a war on drugs 40 years ago, the United States has spent more than a trillion dollars, arrested more than 45 million people, and racked up the highest incarceration rate in the world. Yet it remains laughably easy to obtain illegal drugs. So why do we continue down this same path? Why do we talk about the drug war as if it's a success? It's a charade..."

Pitt recently threw his support behind U.S. President Barack Obama after the politician insisted police won't be "going after recreational users" in states that have declared marijuana legal for medical purposes, because they have "bigger fish to fry".