Prescription drug monitoring needed post-MBS

Bariatric patients may need closer monitoring of their prescription medications post-surgery to avoid risk of harm, according to researchers at King’s College London. Their study found that bariatric surgery patients face unique risk factors relating to overdose. This is because the surgical changes to their stomach and intestine to reduce food and nutrient absorption, can also affect how they absorb drugs.

By examining data from the National Programme of Substance Use Mortality (NPSUM), the researchers conducted the first toxicology-based investigation of overdose deaths in post-bariatric surgery patients. Multiple medications - including opioids, antidepressants and common painkillers - were detected at post-mortem in every case, and often included medications that the deceased were not actively prescribed.

Opioids were found to have contributed to the deaths of nearly every person, while antidepressants were implicated in the deaths of just under half. Unlike many cases on the NPSUM database, illicit drug and alcohol use was rare. Together, this highlights how chronic pain and mental health conditions leave this group particularly vulnerable to prescription-medication harm.

“Our research highlights a gap in care that is readily addressable. Post-bariatric surgery patients are frequently seen by their clinicians in routine follow-up appointments, into which advice about drug safety could be integrated,” explained the study’s lead author. Dr Caroline Copeland, Senior Lecturer in Pharmacology & Toxicology, King’s College London. “Embedding pharmacist-led medication reviews into standard follow-up could prevent avoidable overdose deaths in this vulnerable group.”

While bariatric surgery can be a powerful tool in reducing excess weight, previous studies have highlighted how these significant surgical changes can unpredictably alter the pharmacokinetics of gastrointestinal system, influencing how drugs are absorbed. While this differs from person to person - depending on the type of surgery, the drug involved, and other factors - these pharmacokinetic changes can increase the potency of drugs, or alternatively, decrease the potency, leading to repeated dosing.

The researchers identified 18 people with a history of bariatric surgery whose deaths were noted in the NPSUM records between 1997 and 2025. Coroners voluntarily report a death to NPSUM if psychoactive drugs were detected or implicated in causing the death, or if the deceased had a history of drug use.

Opioids were detected and contributed to the deaths of 94.4% (17 out of 18) of cases, compared to an average of just 67% across all 58,000 cases on the NPSUM database. Non-opioid analgesics, which include drugs such as paracetamol and ibuprofen, were found in 72.2% (13/18) of cases. The prevalence of these medications suggest that this patient group faces chronic pain and has risks around medication to manage this. Depression and anxiety were common in this group, and antidepressants were identified in 83.3% (15/18) of cases and found to have contributed in just under half of deaths.

The combination of mental health diagnoses and chronic pain suggest polypharmacy – when an individual is on multiple medicines at once - could be a problem, leading to higher risk of side effects and drug interactions. The average number of drugs detected at post-mortem was six.

Coroners had determined that 75% of individuals had died of accidental overdose. This closely aligns with the NPSUM database, where 76% of deaths are classified as accidental. However, while illicit drugs and alcohol frequently contribute to deaths in the wider NPSUM dataset, such involvement was rare among the post-bariatric surgery cases.

The researchers call for more work to be done to better understand how surgery changes the pharmacokinetics of the gastrointestinal system and therefore the way drugs are absorbed. They also suggest that a clinical pharmacist is involved in discussions before surgery takes place, and that drug monitoring continues for patients following their surgery.

“It isn’t clear the extent to which healthcare providers in the UK include routine assessment of medicines before and after bariatric surgery. However, the deaths link to prescription medicines outlined in this study suggest that there is a need for this,” added a co-author of the study, Dr Alice Oborne, Medicine Safety Lead, Guy’s and St Thomas’ NHS Foundation Trust. “Clinical pharmacists are in a good position to review medicines after bariatric surgery considering the ongoing changes in pharmacokinetics and how patients respond to drugs, their side effects, drug-drug interactions and other adverse drug reactions.”

The findings were reported in the paper, ‘Drug poisonings following bariatric surgery: Case series report’, published in the British Journal of Clinical Pharmacology. To access this paper, please click here