For example, Likhitsup's group estimated that more than 11 million adults regularly take turmeric supplements, often with the notion that it can ease pain or arthritis. That's not too far below the approximately 14.8 million who take an NSAID pain reliever for much the same reasons.

Unfortunately, "multiple randomized clinical trials have failed to demonstrate any efficacy of turmeric-containing products in osteoarthritis," and overdoing it on turmeric has been linked to serious liver toxicity, the researchers said.

People taking botanicals were more likely to be battling some kind of chronic illness, such as arthritis, thyroid disorders or cancer, compared to folks not using the supplements.

In two-thirds of cases, people took a botanical while also taking a prescription medicine, the study found. Because of the danger of drug interactions and the threat to liver health, it's crucial that botanical users inform their doctors, Likhitsup's group said.

When botanicals are overused, the damage to the liver "can not only be severe, leading to hepatocellular [liver] injury with jaundice, but also fatal, leading to death or liver transplantation," the research team warned.