One in five adults who undergo weight-loss surgery will get hooked on prescription painkillers for years after, alarming new statistics show.

Although most patients wean themselves off their post-operation pills in a matter of months, figures show a fifth of them will gradually return to them within a matter of years.

In fact, patients are more likely to pick up the habit even if they were not prescribed potentially addictive opioids during their recovery period, according to the data compiled by the University of Pittsburgh Graduate School of Public Health.

Many patients undergo bariatric surgery to alleviate obesity-related pain in their joints and organs.

However, the researchers warn this study - one of the largest, longest-running studies of adults who underwent weight-loss surgery - shows the operation may not be enough to curb that pain and prevent painkiller addiction.

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Although most patients wean themselves off their post-operation pills in a matter of months, figures from the University of Pittsburgh show a fifth will gradually return to them within a matter of years

'Almost half of patients reporting opioid use at the time of surgery reported no such use following surgery,' said lead author Dr Wendy C. King, associate professor of epidemiology at Pitt Public Health.

'However, among the much larger group of patients who did not report opioid use pre-surgery, opioid use gradually increased throughout seven years of follow-up.

'Thus, post-surgery initiation of opioid use explains this phenomenon.'

The CDC recently presented an evidence-based guideline stating that opioids should not routinely be used to manage chronic pain.

However, the Pitt study shows the rate of patients using opioids is far higher seven years later than when they initially got treatment for weight loss.

Starting in 2006, King and her colleagues followed more than 2,000 patients participating in the NIH-funded Longitudinal Assessment of Bariatric Surgery-2 (LABS-2), a prospective observational study of patients undergoing weight-loss surgery at one of 10 hospitals across the United States.

About 70 percent of the patients underwent Roux-en-Y gastric bypass (RYGB), a surgical procedure that significantly reduces the size of the stomach and changes connections with the small intestine.

The majority of the remaining participants had a less invasive procedure, laparoscopic adjustable gastric banding, where the surgeon inserts an adjustable band around the patient's stomach, lessening the amount of food the stomach can hold.

TYPES OF WEIGHT LOSS SURGERIES The three most common weight loss surgeries are lap band, gastric sleeve and gastric bypass operations. LAP BAND A lap band procedure is an inflatable band placed around the top of the stomach, restricting food intake. The average cost is $14,500 and patients lose around 10 percent of their original body weight. Pictured: An illustration of lap band surgery GASTRIC SLEEVE The gastric sleeve is a non-reversible procedure and involves removing 80 percent of the stomach. It stabilize gut hormones which are off-balance in obese people, driving them to crave food when they don't need it. The average cost is $15,000 and patents lose around 17 percent of body weight. GASTRIC BYPASS Gastric bypasses divides the stomach into a small upper pouch and a much larger pouch. The surgeon rearranges the small intestine to connect to the small pouches. The average cost is $23,000 and patients lose around 27 percent of body weight. Advertisement

Before surgery, 14.7 percent of the participants reported regularly taking a prescription opioid. Six months after surgery the prevalence decreased to 12.9 percent, but then it rebounded, progressing to 20.3 percent of participants regularly taking opioids seven years after surgery.

Among participants who were not taking opioids at the time of surgery, rates increased from 5.8 percent six months after surgery to 14.2 percent seven years later. Hydrocodone was by far the most commonly reported opioid medication, followed by Tramadol and Oxycodone.

There also was an increase over time in the use of medications typically prescribed for opioid dependence, although use of such medications remained rare, with less than 2 percent of patients using them through the years of follow-up.

'Our nation is in an epidemic of opioid abuse, addiction and overdose. Recent reports have suggested that bariatric surgery patients are at elevated risk of chronic opioid use,' said co-author Dr Anita P. Courcoulas, chief of minimally invasive bariatric and general surgery at UPMC.

'Our study does not prove that bariatric surgery causes an increase in opioid use. However, it does demonstrate the widespread use of opioids among post-surgical patients, thereby highlighting the need for alternative pain management approaches in this population.'

The risk of starting or continuing opioid use post-surgery was the same after every version of weight-loss surgical procedures.

The researchers found this urge to take opioids were not affected by the typical factors, such as gender, age, income, social support, or mental health.

Rather it was driven more by pain before surgery, and slow improvement in pain following surgery.

Some researchers have hypothesized that opioid use increases following bariatric surgery due to discontinuation of non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, which are contraindicated post-surgery.

However, King and her colleagues found that starting NSAIDs post-surgery was associated with a higher risk of also starting to take opioids, while stopping NSAIDs was associated with lower risk of taking opioids.

'This likely reflects that opioid and non-opioid pain-relief medications often are used in tandem, versus as alternatives to each other,' said King. 'There is an urgent need for research into adequate alternatives to opioids for the long-term management of chronic pain following weight-loss surgery.'