Bitter orange, which is used in weight loss supplements, has been linked to heart attack and stroke. Another common ingredient, coltsfoot, has been tied to cancer and liver damage. Not all dietary supplements are dangerous. Many are probably harmless. Some may actually perform as advertised. But very few studies have tested their effectiveness. And existing studies don’t do much to support the claims of dietary supplement makers and marketers. Because dietary supplements are regulated very lightly, you can buy as much as you want, over the counter. But that doesn’t mean you should. The packaging may promise tempting health benefits. But when it comes to the safety of dietary supplements, there’s a lot that scientists don’t know.