Turmeric has done the full circle: from ancient remedy to hipster Western drink.
Even today, Indians readily apply it on fresh wounds, chicken-pox scabs, and insect bites. Medical professionals prescribe it for urological diseases, worm infections, and even cancer. Such has been the hype that the yellow-golden spice is widely touted as a validation of traditional medicine.
Scientists have now had enough. Turmeric’s gains have been ascribed to a chemical contained in it called curcumin. But, though there have been thousands of research papers and 120 clinical trials, curcumin hasn’t yet resulted in a drug.
In a new review of chemical evidence, scientists write that curcumin is an “unstable, reactive, non-bioavailable compound and, therefore, a highly improbable lead [for drug development].” The reason for this notorious review is because of its chemical properties that mess with leading methods to search for new drugs.
Most drugs are screened based on their ability to interact with certain proteins. It turns out curcumin’s chemical structure makes it produce “false hits” – that is, even though the compound doesn’t interact with the protein, the results of studies show that it does. Such false hits are then taken to clinical trials, where, after spending huge amounts of money, it eventually fails.
“Curcumin is a cautionary tale,” Michael Walters of the University of Minnesota in Minneapolis told Nature. Cautionary because curcumin falls in a category of compounds, appropriately named PAINS (for pan-assay interference compounds), known to produce such false results.
Inside the body, curcumin breaks down into chemicals which have different properties. Sometimes it is contaminated with other compounds that have their own biological activity, which gets falsely ascribed to curcumin. It even becomes fluorescent when ultraviolet light is shone on it, which fools a common scientific technique used to detect if a chemical is interacting with a specific protein.
“Much effort and funding has been wasted on curcumin research,” Gunda Georg, co-editor-in-chief of the Journal of Medicinal Chemistry, which published the review, told Nature. At least 15 studies on curcumin have been retracted from scientific literature, and dozens more have had corrections appended to them.
And, yet, most people working in the field aren’t aware of the mischievous properties that curcumin has. Georg still receives regular submissions on curcumin research.
The effects that turmeric may have on, say, a sore throat, could simply be placebo effects. That is to say, the act of going into self-care mode and drinking a hot, comforting drink is what results in healing rather than any direct effect of the turmeric.
Not everyone has given up hope. Julie Ryan of University of Rochester Medical Center failed to show in a clinical trial that curcumin could treat dermatitis. And, yet, she believes that the compound deserves more study.
Turmeric is made of hundreds of chemicals and Walters isn’t hopeful of getting real results. “It may very well be the case that curcumin or turmeric extracts do have beneficial effects, but getting to the bottom of that is complex and might be impossible,” he told Nature.
His point is valid. The resources being wasted on difficult curcumin research could instead be spent on thousands of other chemicals lying on shelves waiting to be tested.
This article first appeared on Quartz.