More than two millions Britons taking a popular antidepressant have been urged to watch out for signs of a dangerous condition after packets of the medication were mistakenly mixed with doses of a different drug.
Sertraline users have been warned to ‘seek medical help immediately’ if they experience a fast heart beat, nausea, headache or sleep changes.
The symptoms could be a sign of a life-threatening reaction known as serotonin syndrome – caused by mixing or alternating two types of antidepressant.
The potentially dangerous condition can also present as confusion, agitation, sweating and shaking, according to the NHS website.
In severe cases, it can even lead to coma, a prolonged state of deep unconsciousness.
The warning comes amidst a large-scale recall of a batch of sertraline packets found to also contain tablets of citalopram, another commonly prescribed antidepressant.
Britons taking 100mg film-coated tablets with batch number V2500425 and an expiry date of May 2028 were urged on Tuesday to check their medicine for strips of citalopram.
Anyone finding rogue strips of the drug has been advised to contact their pharmacy immediately.
The 2million people who take sertraline (stock image) every year have been urged to check their medicine after a batch was found to contain citalopram
Both sertraline and citalopram are selective serotonin reuptake inhibitors (SSRIs) – widely prescribed drugs used to treat depression, anxiety and other mood disorders by boosting serotonin in the brain.
But alternating or combining SSRIs can be dangerous – and even deadly – say experts.
Speaking about the recall on Tuesday, Dr Alison Cave, Medicines and Healthcare products Regulatory Agency (MHRA) chief safety officer, said: ‘Patients who have accidentally taken citalopram instead of – or as well as – sertraline, may experience some heightened serotonergic side effects.’
Official NHS guidance states that symptoms of serotonin syndrome can range from mild to severe and should be treated urgently.
Physical symptoms can show in the form of hypertension – known as high blood pressure – as well as a tachycardia, which is when the heart rate rises over 100 beats per minute – and hyperthermia, which causes the body’s temperature to rise to around 40C.
Other warning signs include dry eyes, unusually active bowel sounds, excessive sweating, tremors and clonus – involuntary, rhythmic muscle contractions.
Patients may also experience muscle and joint stiffness, along with hyperreflexia, where reflexes become unusually exaggerated.
Meanwhile, mental symptoms can bring on feelings of anxiety, agitation and confusion. Worryingly, in the most serious cases the condition can lead to coma, a prolonged state of deep unconsciousness.
Fears were recently sparked over the side effects of mixing variations of the tablets following the high-profile suicide of Lady Gabriella Windsor’s former husband Thomas Kingston in February 2024.
Mr Kingston, 45, whose marriage to Lady Gabriella at Windsor Castle in 2019 was attended by the late Queen, shot himself after being prescribed the drugs sertraline and citalopram for anxiety by a Buckingham Palace doctor.
In a prevention of future deaths report published last year, senior coroner Katy Skerrett raised concerns over whether there is ‘adequate communication’ regarding the risks of suicide with such pills.
She also questioned whether the current guidance on whether to ‘persist’ with the drugs was ‘appropriate’ in circumstances when ‘adverse side effects’ are experienced.
More than 40 other prevention of future deaths reports have referenced the use of either citalopram or sertraline by the deceased person.
The reports raised a range of concerns – such as a failure to alert patients to potential side-effects, breaches of prescribing guidelines, not reviewing patients and not keeping records of patients’ behavioural changes while on the medication.
The manufacturing company of the recalled batch of sertraline has received one complaint from an adult patient who reported the adverse event of a headache, where it was identified that their prescription wrongly contained a strip of Citalopram tablets.
Both drugs were manufactured at the same site, and the error appears to have occurred during secondary packing of the strips into the carboard packaging.
Lady Gabriella’s former husband Thomas Kingston (right) died by suicide in 2024 after taking citalopram soon after stopping setraline
Pharmacists and other healthcare professionals involved in dispensing the antidepressant have also been advised to contact any patients who may have been given the wrong medication and request it be returned.
The affected batch was first distributed on November 28, 2025.
GPs and clinicians should then be made aware of the mix-up to discuss treatment review and whether a new prescription may be required for ongoing resupply.
Patients aged over 65 or under 18, as well as those with heart of liver conditions need to be particularly cautious, the MHRA warned.
Any suspected adverse reactions should also be reported via the watchdog’s Yellow Card scheme.
The MHRA has advised healthcare professionals to stop supplying the affected batch and return all remaining stock to their suppliers.
For confidential support, call Samaritans on 116 123, visit samaritans.org or visit https://www.thecalmzone.net/get-support
