Major review confirms GLP-1 safety for weight loss

The study

October 2025, Nature Medicine. McGowan, Ciudin, Baker and co-authors published the largest systematic review and network meta-analysis of obesity management medications to date — covering 56 randomised controlled trials enrolling 60,307 patients across six drug classes.

The review included 14 trials of semaglutide, 11 of liraglutide, 6 of tirzepatide, alongside orlistat (22 trials), naltrexone/bupropion (5), and phentermine/topiramate (2). The primary endpoint was percentage total body weight loss at study end. Secondary endpoints covered metabolic outcomes, cardiovascular events, adverse effects, and quality of life.

Key findings:

• All obesity medications showed significantly greater weight loss than placebo (p < 0.0001).
• Semaglutide and tirzepatide achieved the largest effects, with mean weight loss exceeding 10% of total body weight — a clinically meaningful threshold associated with improvements in obesity-related complications.
• Semaglutide reduced major adverse cardiovascular events and improved pain in knee osteoarthritis.
• Tirzepatide was effective in achieving remission of type 2 diabetes, obstructive sleep apnoea, and metabolic dysfunction-associated steatohepatitis (MASH).
• Serious adverse event rates were comparable between active treatment and placebo groups across all drug classes, with gastrointestinal side effects being the most commonly reported — consistent with the known tolerability profiles of GLP-1 receptor agonists.

The UK connection is significant: the first author, Dr Barbara McGowan, is a consultant endocrinologist at Guy's & St Thomas' Hospital NHS Trust in London and a shareholder in Reset Health, a digital weight-management provider. The review was conducted under the auspices of the European Association for the Study of Obesity (EASO).

Why it matters for regulation

This review provides the strongest available evidence that GLP-1 receptor agonists, when prescribed in accordance with clinical guidelines, have a well-characterised safety profile. For UK regulators and clinic operators, the implications are threefold:

First, the evidence supports NICE's current framework. NICE guidance NG246 recommends GLP-1 medicines as adjuncts to lifestyle intervention in defined BMI categories, with continuation criteria requiring at least 5% weight loss at 12 weeks. This review — showing >10% mean weight loss for semaglutide and tirzepatide — confirms those thresholds are clinically appropriate.

Second, safety concerns should not drive over-regulation. As the GPhC tightens oversight of online weight-loss prescribing — its April 2026 inspection review identified gaps in assessment and monitoring — this evidence base helps distinguish between medicine-specific risk and provider-specific failures. The medicine is safe when prescribed properly; the regulatory focus should remain on the quality of the prescribing pathway, not the molecule itself.

Third, the findings support Yellow Card vigilance. The review found no unexpected safety signals across 60,000+ patients. But the real-world prescribing environment — particularly online commercial models — differs from tightly controlled RCT settings. The MHRA's Yellow Card scheme remains the primary surveillance mechanism for detecting rare or long-term adverse events that may only emerge in broader populations.

For clinics and pharmacies prescribing GLP-1 medicines, the message is clear: the clinical evidence base for these treatments is robust and expanding. Regulatory scrutiny on prescribing practices — assessment quality, monitoring, continuity — is appropriate and necessary. But the treatments themselves are supported by high-quality evidence.

Key takeaway

The largest meta-analysis of obesity medications to date — including UK clinical expertise from Guy's & St Thomas' — confirms that semaglutide and tirzepatide achieve clinically meaningful weight loss with a safety profile consistent with existing regulatory approvals. For clinic owners and compliance teams, this strengthens the case for investing in robust prescribing pathways rather than questioning the treatments themselves.