Over the last few years, a new class of medicines have taken the weight-loss market by storm. Novo Nordisk's Wegovy and Eli Lilly's Zepbound both belong to a group of drugs known as GLP-1 receptor agonists, which mimic hormones involved in appetite regulation and help patients feel fuller for longer. The results have been remarkable, with clinical trials demonstrating levels of weight loss previously associated primarily with bariatric surgery.1

Average weight loss achieved across obesity interventions (%). Approximate figures compiled from major clinical trials and published reviews.

Comparison caveat: These figures are drawn from separate trials and reviews with different patient populations, durations, and designs - they are not head-to-head results. Cross-intervention comparisons are indicative only and should be interpreted with care.

These outcomes have transformed expectations of what obesity medicines can achieve and helped fuel one of the largest growth stories in modern healthcare.

As global obesity rates continue to climb, analysts estimate the market for obesity therapeutics could exceed $100 billion annually, turning Novo Nordisk and Eli Lilly into two of the most closely watched companies in global healthcare.2

Most discussions focus on a single question: who will win the obesity drug race?

This may be the wrong question entirely.

Both firms have already demonstrated that meaningful weight loss is possible. The greater uncertainty lies not in how much weight a patient can lose, but in what happens afterwards, over the long run. Clinical evidence suggests weight gain can occur following treatment discontinuation, raising an uncomfortable possibility for investors: the long-term value of the obesity market may depend less on how many patients start therapy and more on how many remain on it.3

The defining risk facing the GLP-1 boom is not competition. It is sustainability.

The Sustainability Problem

The investment case for GLP-1 therapies ultimately depends on a single assumption: patients remain on treatment.

This may be more challenging than it appears. Obesity is increasingly being recognised as a chronic disease, yet many patients view weight loss as a destination rather than an ongoing process. Once patients have achieved their target weight, the incentive to continue treatment naturally declines.

The evidence suggests this matters. In the STEP 1 extension study, participants regained approximately two-thirds of their weight loss within a year of discontinuing semaglutide.4 While the treatments remain effective, maintaining those benefits appears considerably harder once therapy ends.

This creates an uncomfortable question for investors. If a meaningful proportion of patients discontinue treatment after achieving weight loss, can current revenue expectations be sustained?

If obesity is ultimately managed as a chronic disease rather than a temporary intervention, the industry's economics may resemble long-term maintenance therapy more than traditional weight-loss treatment.

Why Investors Should Care

For investors, weight regain is more than a clinical observation; it is a valuation question.

The obesity market is often discussed in terms of patient adoption, market share, and competitive positioning. Yet long-term revenue depends not only on how many patients begin treatment, but on how long they remain on it.

A patient who remains on therapy for several years generates substantially more value than one who discontinues treatment after achieving their target weight. If treatment continuation rates fall below expectations, projected revenues may prove less predictable than current growth assumptions.

Thus the greatest risk facing Novo Nordisk may not be Eli Lilly. It may be the gap between clinical efficacy and long-term adherence.

Closing the Adherence Gap

Both Novo Nordisk and Eli Lilly are investing heavily in the next generation of obesity treatments, with the goal of improving both efficacy and long-term adherence.

One avenue is convenience. Oral formulations, such as Novo Nordisk's oral semaglutide, could remove the burden of weekly injections and make treatment more accessible to patients reluctant to commit to injectable therapies.

Another is efficacy. Combination therapies targeting multiple metabolic pathways are being developed with fewer side effects, which may help reduce discontinuation rates.5

Final Thought

The obesity market will not be won on efficacy alone. The company that solves long-term adherence may capture the greatest clinical impact - and the largest share of a market expected to exceed $100 billion.

Footnotes

  1. Wilding JP, Batterham RL, et al., Once-Weekly Semaglutide in Adults with Overweight or Obesity, New England Journal of Medicine (opens in a new tab), 2021; Jastreboff AM, Aronne LJ, et al., Tirzepatide Once Weekly for the Treatment of Obesity, New England Journal of Medicine (opens in a new tab), 2022. ↩

  2. Morgan Stanley, Scaling Up the Impact of Obesity Drugs, Morgan Stanley (opens in a new tab),2024 ↩

  3. Rubino D, Abrahamsson N, et al., Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial, JAMA (opens in a new tab), 2021. ↩

  4. Wilding JP, Batterham RL, et al., Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension, Diabetes, Obesity and Metabolism (opens in a new tab), 2022. ↩

  5. GLP-1 single, dual and triple receptor agonists for treating type 2 diabetes and obesity: a narrative review, ResearchGate (opens in a new tab), 2024. ↩