Over two million Britons prescribed the popular antidepressant sertraline have received an urgent warning to monitor for signs of a life-threatening condition after a manufacturing error led to packets being mixed with another antidepressant, citalopram. Users have been advised to seek immediate medical help if they experience symptoms such as a fast heart beat, nausea, headache, changes in sleep patterns, confusion, agitation, excessive sweating, or shaking. These symptoms could indicate serotonin syndrome, a dangerous reaction caused by combining or alternating certain types of antidepressants.

The warning follows a large-scale recall of specific batches of sertraline. Patients taking 100mg film-coated tablets with batch number V2500425 and an expiry date of May 2028 are urged to check their medication for strips of citalopram. Anyone discovering rogue strips of the incorrect drug must contact their pharmacy without delay. The Medicines and Healthcare products Regulatory Agency (MHRA) has stated that patients who have accidentally ingested citalopram instead of, or in addition to, sertraline may experience heightened serotonergic side effects.

Both sertraline and citalopram are selective serotonin reuptake inhibitors (SSRIs), which are commonly prescribed to treat depression, anxiety, and other mood disorders by increasing serotonin levels in the brain. However, medical experts warn that alternating or combining these SSRIs can be dangerous, potentially leading to severe complications or even death. Serotonin syndrome symptoms can range from mild to severe, requiring urgent medical intervention.

Physical manifestations of serotonin syndrome can include hypertension (high blood pressure), tachycardia (heart rate exceeding 100 beats per minute), and hyperthermia (body temperature rising to around 40°C). Other critical signs may involve dry eyes, unusually active bowel sounds, excessive sweating, tremors, clonus (involuntary, rhythmic muscle contractions), muscle and joint stiffness, and hyperreflexia (exaggerated reflexes). Mentally, patients may experience anxiety, agitation, and confusion. In its most severe form, the condition can progress to a coma, a prolonged state of deep unconsciousness.

The risks associated with mixing antidepressants gained prominence following the high-profile suicide of Thomas Kingston, Lady Gabriella Windsor's former husband, in February 2024. Mr. Kingston had been prescribed sertraline and citalopram for anxiety. A prevention of future deaths report subsequently raised concerns regarding the adequacy of communication about suicide risks associated with such medications and the appropriateness of guidance on persisting with drugs when adverse side effects are experienced. Over 40 other prevention of future deaths reports have referenced the use of either citalopram or sertraline by deceased individuals, highlighting issues such as failure to alert patients to side effects, breaches of prescribing guidelines, and insufficient patient reviews or record-keeping of behavioural changes.

The manufacturing error, which led to the sertraline batch recall, is believed to have occurred during the secondary packing stage where strips of different drugs were inadvertently placed into the cardboard packaging. The company responsible has reported one complaint from an adult patient who experienced a headache after their prescription wrongly contained a strip of citalopram tablets.

Pharmacists and other healthcare professionals involved in dispensing these antidepressants have been instructed to contact any patients who may have received the affected medication and arrange for its return. The problematic batch was initially distributed on November 28, 2025. GPs and clinicians must be informed of the mix-up to facilitate treatment reviews and potentially new prescriptions. Special caution is advised for patients over 65, under 18, or those with existing heart or liver conditions. Any suspected adverse reactions should be reported via the MHRA's Yellow Card scheme, and healthcare professionals have been advised to cease supplying the affected batch and return all remaining stock to suppliers. For confidential support, individuals are encouraged to contact Samaritans or The Calm Zone.