Patients are being put at risk because their drug allergies are not flagged up by hospital staff, research suggests.
Patients should be asked about allergies on admission
Those with a known allergy are supposed to be given a red hospital identification bracelet to warn staff.
But University of Sunderland studies found this happened in less than half of patients and in many cases allergy status was not recorded in the notes.
Experts said the findings presented at the British Pharmaceutical conference in Manchester were "worrying".
In one study of almost 400 patients the Queen Elizabeth Hospital in Gateshead, many patients who were known to have a drug allergy were not issued with the red bracelet as per hospital policy, although figures were better in patients being admitted for planned surgery.
Overall three-quarters of patients patients' had no record of drug allergy status in their clinical notes or on their drug charts, making it unclear whether the question had been asked.
A separate study if 100 patients on an elderly admissions ward at City Hospital Sunderland, also carried out by University of Sunderland researchers, also found that the recording of allergy status was incomplete or sometimes overlooked or omitted.
The researchers looked at the pharmacists records, the clinical notes and the electronic prescribing system, which should all have a record of any allergies.
In nearly 40% of patients with a known drug allergy the allergic reaction was not recorded.
And where there was a record, the entries were more likely to be made by pharmacists, rather than doctors.
A report from the Royal College of Physicians published in 2003 found up to 15% of inpatients have a longer hospital stay than expected as a result of drug allergy.
Dr Rachel Etherington, who led the research at City Hospital Sunderland said hospital pharmacists were well placed to make sure of allergy status was recorded and should perhaps have a greater role.
She added although the study was small, patients were being missed and that translated to a large number when all hospital admissions were taken into account.
"There are inconsistencies.
"It's important the doctor knows about the allergy and what type of allergic reaction the patient has had," she said.
Andrew Husband, principle lecturer in pharmacy at the University of Sunderland and lead on the Gateshead study said allergies were a significant cause of avoidable adverse drug reactions among hospital in-patients each year.
"The solution is to increase awareness among hospital staff of the importance of this issue.
"Every member of a hospital multi-professional team is responsible for ensuring that drug allergy status procedures are followed."
Muriel Simmons, chief executive of Allergy UK said the findings were disgraceful.
"It's extremely worrying. We are seeing a rise in drug allergies so it makes it more important that doctors are on the ball when it comes to the warning band.
"We would certainly advise people to insist on the red band.
"If a patient is unconscious and their drug allergy isn't recorded it can be fatal."
A spokesperson for Gateshead Health Trust said it was small study.
"What it suggests contrasts markedly with a recent survey undertaken by the Trust's own staff where a compliance rate of well over 90% was demonstrated."