Bacteria in the gut are partly to blame for the horrible side-effects of chemotherapy, scientists in the US have found.
And disabling the bacteria doesn't appear to affect the effectiveness of the cancer drugs.
"Gastrointestinal microbiota are the great crowd-sourcers of chemistry, using a dizzying array of enzymes to process drugs and other chemicals, occasionally with terrible consequences," says senior study author Matthew Redinbo of the University of North Carolina.
Side-effects such as diarrhoea happen when bacteria in the gut process chemicals marked for elimination from the body. The process releases a "virulently toxic" drug into the intestines, causing diarrhoea in 90 percent of patients taking drugs such as irinotecan.
Tests on mice show the bacteria which cause the problems can be inhibited, without affecting irinotecan's ability to fight cancer.
Dr Redinbo says the findings provide a "promising new set of targets for controlling drug-induced gastrointestinal toxicity", and could also help make other drugs – such as non-steroidal anti-inflammatories like Voltaren – easier to ingest.
The study is published today in journal Chemistry & Biology, and follows research last year which suggested some cancer drugs work better with higher concentrations of bacteria.