Coffee contains acrylamide, a chemical found in many foods that are cooked to very high temperatures, and which some studies have found is a carcinogen, especially if consumed at very high quantities.
Under proposition 65, California state law requires businesses with 10 or more employees to provide reasonable warning about the use of any chemicals that could cause cancer, birth defects or reproductive problems.
Now superior court judge Elihu Berle has ordered Starbucks and other coffee chains to display warnings after they had failed to demonstrate that the risks were "insignificant".
That's surprising, because there is plenty of evidence out there to show just that. One study, by the University of Milan, demonstrated that not only does coffee not cause cancer, it protects against several types, including liver and endometrial cancers, and there was less compelling, but still good, evidence it protects against oral and pharyngeal cancers as well.
At worst, the International Agency for Research on Cancer has stated that coffee is "a possible carcinogenic to humans"—but has said subsequently there's no evidence that it causes bladder cancer, while the World Cancer Research Fund confirmed that some cancers, including liver, were less common in coffee drinkers.
Many were 'lifestyle' studies and failed to factor in other—and accepted—causes of cancer, such as smoking, diet and obesity, pollutants and heavy drinking.
So—should you give up the morning brew? The short answer is no, but don't switch to it from tea if you don't already drink it!