People who regularly take slightly too much paracetamol over a period of time to relieve pain could be at a higher risk of dying than those who take a one-off overdose of the drug, a study revealed yesterday.

The danger arises because the so-called staggered overdoses are more difficult for doctors to assess and therefore treat.

The research, published in the British Journal of Clinical Pharmacology, showed that doctors usually take a blood sample to detect how much paracetamol is present when an overdose patient arrives at hospital.

For someone who has taken too much of the drug over a prolonged space of time, low levels of paracetamol could be detected in their blood even though they could still be at risk of organ failure or death.

Kenneth Simpson, medical doctor who worked with the University of Edinburgh and the Scottish Liver Transplantation Unit, said: “They haven’t taken the sort of single-moment, one-off massive overdoses taken by people who try to commit suicide, but over time the damage builds up, and the effect can be fatal”.

Patients are also less likely to report a staggered overdose to medical staff than a massive single overdose, the research team said.

They looked at data from 663 patients admitted to the Royal Infirmary of Edinburgh from 1992 to 2008 with liver injury caused by Paracetamol. Of those patients, a total of 161 had suffered a staggered overdose, mostly after taking the drug to relieve common pains including headaches and stomach pains.