Experts have raised concerns that flawed analysis of drug levels in corpses could affect the outcomes of court cases and inquests.
Blood drug levels in corpses should be interpreted carefully, say experts
The international team writing in the British Medical Journal says this leads to confusion and conspiracy theories.
They cite the death of weapons expert David Kelly as a high profile case where differences of opinion have been expressed over drug results.
However, they say there is no dispute over Mr Kelly's cause of death.
The comments of the experts from the International Toxicology Advisory Group show renewed concern over how such results are interpreted in countries around the world.
In March, US and UK experts warned the level of drugs in the blood can increase by 15-fold when someone dies because the toxins are released into the bloodstream.
In the BMJ editorial, the forensic medicine experts warn problems can arise because, unlike in cases involving living patients, toxicology tests after death can virtually never be informed by information about how drugs were administered and number of doses taken.
In addition, if a person has been a chronic drug user, and has developed a 'tolerance', it can be factored into toxicology measurements for living patients but cannot be measured in dead bodies.
But the experts warn that, despite these concerns, in some cases conclusions continue to be drawn based on comparisons with living subjects, or by looking at measurements alone, without examining the case as a whole.
They warn such specific measurements are not an accurate guide because factors in individual cases can affect how they should be interpreted.
Derrick Pounder, Professor of Forensic Medicine at Dundee University. one of the authors of the editorial, said: "This is a chronic problem in forensic medicine.
"We know full well that the results of the analysis of drug tests are very difficult to interpret. The drug level in itself is no use. It has to be interpreted in the context of the case."
But he said: "Some individuals still persist in interpreting these results in a very rigid way."
The experts also warn that blood drug concentration levels can vary significantly in dead bodies depending on where the sample is collected from.
Professor Robert Forrest of the University of Sheffield, who is also part of the group which wrote the editorial, said: "For example, a lot of antidepressants, such as amytripiline, are bound to lung tissue.
"So if an old lady was found dead and a sample of heart blood was analysed, the drug concentration level might be 3.5 milligrams per litre. The interpretation of that would be that she'd taken an overdose.
"But if the sample was taken from the femoral vein in her groin, it might have a concentration of 0.35 milligrams per litre, which is entirely consistent with normal therapeutic use."
He and his colleagues warn that, if drug levels at the time of death are impossible to determine, pathologists cannot make judgements on the amount of drugs taken into the body before death.
However these projections are often produced in court as evidence.
Professor John Foster, chairman of the Royal College of Pathology's toxicology science advisory committee, said: "The science underpinning the extrapolation of results is not there.
"Most professionals would acknowledge the problem. But they can perhaps be pushed by the legal profession to go a little bit further than they should be going."
He added: "The underlying message in the article is a call for more honesty in describing the limitations inherent in the science as it exists today .
"These limitations demand a more rigorous approach to extrapolating data obtained from dead bodies until the effect that the death process has on drug concentrations can be better characterised and defined."