One of America's best-known pain relievers has a lesser-known dark side. Over the past decade, more than 1,500 Americans have died from taking too much acetaminophen, the active ingredient in Tylenol, reports ProPublica. Though tens of millions of people reportedly use it weekly without adverse effects, large amounts of the drug can lead to liver damage and other major health issues — a fact that isn't as widely publicized as the drug's potential health benefits.

Unlike other popular pain relievers, the difference between a safe and potentially harmful dose of acetaminophen is very slim, reports ProPublica. The Food and Drug Administration has apparently been aware of the issue for decades, but has moved slowly to address it. As far back as 1977, the administration said that it was "obligatory" that acetaminophen is labeled with a warning that it could cause "severe liver damage." But while that warning eventually found its way onto the drug's packaging, it didn't happen until 2009, and the FDA has even admitted that it moved slowly in addressing the issue.

Acetaminophen may be far less safe than aspirin or ibuprofen

Though acetaminophen isn't unique in causing harm when used improperly, the FDA says that it carries more of a risk than other common drugs, such as ibuprofen and aspirin, according to ProPublica. Acetaminophen has reportedly been linked to more deaths than any other over-the-counter pain reliever, and results in 33,000 hospitalizations each year in the US as well.

There may be no singular reason that the FDA moved so slowly to label acetaminophen's dangers, but ProPublica points to McNeil Consumer Healthcare — the maker of Tylenol — as one of its strongest opponents. Though McNeil would eventually concede on certain issues, including the addition of a liver damage warning to the drug's packaging, it consistently held firm that acetaminophen was by and large a safe drug when used as directed.

ProPublica has a thorough history of acetaminophen's safety, including how the FDA and McNeil have responded over the years. While it notes that the FDA's general tone has changed toward acetaminophen — it's even advertised the importance of knowing what medicines contain it — issues may still remain: though McNeil has decided to reduce its recommended daily dosage, its extra-strength products have continued to grow in popularity, potentially making it easier to overuse the drug.