Two different types of life-saving allergy pens are being urgently recalled over fears they may not actually work.
Medical regulators have withdrawn the devices from the UK market as part of a 'precautionary recall', it emerged today.
Evidence was found that the Emerade 300 and 500 microgram pens may in 'rare' cases 'fail to activate' if they are dropped.
The recall doesn't affect the Emerade 150mcg pens.
The Medicines and Healthcare products Regulatory Agency (MHRA), which polices the safety of medicines used in Britain, was behind the recall.
The MHRA said today that routine testing by its manufacturer identified internal structural issues in some pens.
'Premature activation has also been detected' in some of the 300 and 500 microgram pens after they have been dropped, it added.
This means a dose of adrenaline is delivered too early.
Patients, or carers of patients, who carry the auto-injector pens should immediately contact their GP to obtain a prescription for an appropriate replacement, the MHRA urged.
Pharmacists and pharmacy teams can also help with obtaining new prescriptions and dispensing of new pens.
Patients or carers should then return all Emerade 300 and 500 micrograms auto-injectors to their local pharmacy.
But the watchdog cautioned that patients should only return their pens when they have received a replacement from their pharmacy.
Alternative brands available include either the EpiPen or Jext.
People with potentially serious allergies are often prescribed adrenaline auto-injectors to carry at all times.
These can help stop an anaphylactic reaction becoming life threatening.
They should be used as soon as a serious reaction is suspected, either by the person experiencing anaphylaxis or someone helping them.
Each of the three main brands of adrenaline auto-injector pens are used in slightly different ways.
Instructions are included on the side of each injector pen.
Dr Alison Cave, MHRA Chief Safety Officer, today said: 'Patient safety is our top priority.
'We are taking prompt action to protect patients, following detection of damage to internal components of the Emerade pens if they are dropped, which may mean they activate too early or fail to activate and deliver adrenaline.
She added: 'The Department for Health and Social Care has confirmed that there are appropriate supplies of EpiPen or Jext adrenaline pens available for patients across the UK, however, patients will need to request a new prescription.
'Patients are reminded to carry two pens with them at all times as normal and to contact their healthcare professional when a replacement is due.'
Emerade 300 or 500 mcg adrenaline autoinjectors are manufactured by Pharmaswiss Ceska republika s.r.o. and distributed by Bausch & Lomb UK Limited.