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Top-dose phentermine and topiramate cost-effective for adolescents after five-years

Updated: Sep 14, 2023

A study led by researchers from Columbia University Irving Medical Center, who assessed the cost-effectiveness of a range of anti-obesity medications in adolescents, have concluded that top-dose phentermine and topiramate (Qsymia) as adjunct to lifestyle counselling was estimated to be cost-effective after five years. Interestingly, they noted that semaglutide (Wegovy) is not cost-effective at its current price in the US.

"All obesity medications on the market today are effective: they lead to weight reduction and improvements in health," said Dr Chin Hur, professor of medicine at the Vagelos College of Physicians and Surgeons and professor of epidemiology at the Mailman School of Public Health. "But in the context of the US health system, spending on semaglutide is not an efficient use of resources. The slight increase in weight reduction caused by semaglutide compared to a less expensive alternative (top-dose phentermine/topiramate) does not offset semaglutide's much higher cost when considering cost and effectiveness together."

Obesity treatment with drug therapy and lifestyle counselling is now recommended by the American Academy of Pediatrics for adolescents ages 12 years and older with obesity, and several medications have been approved by the FDA for use in teenagers.

Wegovy, approved in December 2022, was the latest to be authorised, following Saxenda (liraglutide, a drug that targets the same GLP-1 receptor as Wegovy) in July 2022 and Qsymia (a combination of phentermine and topiramate) in 2020. Until now, no studies have compared the cost-effectiveness of obesity medications in adolescent patients.

"We felt this study was both timely and needed with the recent publication of results from the phentermine/topiramate and semaglutide adolescent clinical trials as well as their recent FDA approvals for adolescents," added the study's first author, Francesca Lim, a research analyst on Hur's team within the Columbia Healthcare Innovation Research and Evaluation (HIRE) group.

This latest study projected the health and cost outcomes of four different obesity drugs—semaglutide, liraglutide, mid-dose phentermine and topiramate (7.5 mg phentermine and 46 mg topiramate), and top-dose phentermine and topiramate (15 mg phentermine and 92 mg topiramate) - over 13 months, two years and five years among a hypothetical group of 100,000 adolescents with an initial body mass index of 37.

The researchers used a microsimulation model to project health and cost outcomes of lifestyle counselling alone and adjunct to liraglutide, mid-dose phentermine and topiramate, top-dose phentermine and topiramate, or semaglutide.

The main outcome was quality-adjusted life years (QALYs), costs (2022 US dollars) and incremental cost-effectiveness ratios (ICERs), with future costs and QALYs discounted 3.0% annually. A strategy was considered cost-effective if the ICER was less than $100 000 per QALY gained. The preferred strategy was determined as the strategy with the greatest increase in QALYs while being cost-effective.


The model simulated 100,000 adolescents at age 15 with an initial BMI of 37, of whom 58,000 (58%) were female. At 13 months, they projected a relative BMI change from baseline of 0.4% with lifestyle counselling, −4.3% with liraglutide, −4.8% with mid-dose phentermine and topiramate, −7.1% with top-dose phentermine and topiramate, and −13.3% with semaglutide. By five years, BMI change relative to the natural BMI trajectory (ie, no treatment) was estimated to be −2.2% with lifestyle counselling, −7.4% with liraglutide, −9.5% with mid-dose phentermine and topiramate, −10.8% with top-dose phentermine and topiramate, and −18.5% with semaglutide.

Over 13 months, liraglutide was strictly dominated (ie, cost more and less effective) and mid-dose phentermine and topiramate was extendedly dominated (ie, less effective and higher cost per QALY) compared with top-dose phentermine and topiramate. Top-dose phentermine and topiramate was not cost-effective, with an ICER of $317,010 per QALY gained vs lifestyle counselling. At two years, liraglutide and mid-dose phentermine and topiramate were strictly dominated by top-dose phentermine and topiramate. The ICER of top-dose phentermine and topiramate vs lifestyle counselling decreased to $138,045 per QALY gained.

By five years, top-dose phentermine and topiramate became the preferred strategy, with an ICER of $56,876 per QALY gained vs lifestyle counselling. Over each time horizon, semaglutide was projected to accumulate the most QALYs. However, the ICERs for semaglutide vs top-dose phentermine and topiramate were well above our WTP threshold, ranging from $1.1 to $3.0 million per QALY gained.

The researchers summarised that the cost of Wegovy (about $1,400 per month without insurance coverage) would need to be reduced by 85% to match the cost-effectiveness of top-dose Qsymia.

Lim explained the cost-effectiveness of the drugs evaluated in their study could change as more long-term data becomes available, as the longest study of weight-loss drugs in adolescents only lasted approximately one year: "We need data from studies that collect data for 10 to 20 years before we can fully understand the safety, efficacy, and cost-effectiveness of using these medications in adolescents.”

The study, ‘Cost-Effectiveness of Pharmacotherapy for the Treatment of Obesity in Adolescents’, was published in JAMA Network Open. To access this paper, please click here


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