Scientists testing a small but random sample of donated blood ready for transfusion have discovered that 70 percent contained traces of Xanax.

Writing in the Journal of Pharmaceutical and Biomedical earlier this month, researchers were surprised by the level of pharmaceuticals detected in supposedly clean blood batches—in particular, the concentrations of cough medicine and anti-anxiety medication.

The testing also revealed that all 18 batches of blood contained caffeine, suggesting America’s love of coffee, tea and other caffeinated beverages runs deep.

The purpose of the exercise was to find out the purity of the blood samples before they were used to test a method for examining the effect of botanicals on drug metabolization. Botanicals are plants or plant extracts taken for medical or therapeutic reasons, such as echinacea, CBD oil and ginko.

“From a ‘contamination’ standpoint, caffeine is not a big worry for patients, though it may be a commentary on current society,” co-author Luying Chen, a PhD student at Oregon State University (OSU), said in a statement.

“But the other drugs being in there could be an issue for patients, as well as posing a problem for those of us doing this type of research because it’s hard to get clean blood samples.”

In the end, the researchers had to reject all the blood batches tested except for samples from two donors who had agreed ahead of donation not to drink or eat anything containing caffeine.

Eight of the samples (44 percent) contained an over-the-counter cough medicine called dextromethorphan. Thirteen (72 percent) contained the anti-anxiety medication alprazolam, which is sold under the brand name Xanax.

The researchers also tested the blood for a drug used to treat type 2 diabetes (tolbutamide), but did not find any traces of the medicine in the batches tested.

While an interesting insight into the country’s Xanax habit, the purpose of the research undertaken by Chen and Richard van Breemen, a Professor of Medicinal Chemistry at OCU, was to find out how botanical dietary supplements affect the way drugs are broken down by the body.

Understanding this is important as use of botanicals is increasing. A report published by the American Botanical Council found sales herbal supplements jumped 8.5 percent in 2017, exceeding $8bn for the first time. Demand for botanicals appears to be driven by health and wellness trends and a growing preference for natural health products, according to Research and Markets.

“Botanicals basically contain natural products with drug-like activities,” said van Breemen. This means they can affect enzymes in the body just in the same way as manufactured drugs can—an interaction that can cause problems in terms of drug-metabolization in people who take both. It is estimated that almost half of all adults in the U.S. use prescription medications.

The way prescription drugs and botanicals interact is “not straightforward or necessarily predictable,” says van Breeman. “The odd thing in this case was finding all the tainted blood.

“Another thing to consider is that we found drugs that we just happened to be looking for in doing the drug interaction assay validation—how many others are in there too that we weren’t looking for?”

Ultimately, the study involved a relatively small sample of blood. This means it may be hard to infer how widespread the problem of drug contamination in donated blood really is without further testing on a much larger sample size from a diverse range of sources.