Searches for GLP-1 weight loss injections, Mounjaro vs Wegovy, and how Semaglutide works have surged in the past two years. But beyond headlines and social media trends, what does the science actually say?
This evidence-based guide explains how these medications work, how they differ, and what you should know before starting treatment.
GLP-1 (glucagon-like peptide-1) receptor agonists mimic a natural gut hormone involved in:
| 01 | Appetite regulation |
| 02 | Blood glucose control |
| 03 | Slowing gastric emptying |
| 04 | Signalling satiety to the brain |
They were originally developed for type 2 diabetes but are now licensed for weight management in people with obesity or weight-related medical conditions.
Two of the most prescribed options are:
Wegovy contains Semaglutide, a GLP-1 receptor agonist.
It works by:
~15%
average body weight loss over 68 weeks in the STEP clinical trial programme
In the STEP clinical trial programme published in the New England Journal of Medicine, participants lost on average ~15% of body weight over 68 weeks when combined with lifestyle support.
(See: Wilding et al., 2021)
Backlink reference: Wilding JPH et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity." NEJM. 2021.
Mounjaro contains Tirzepatide, which activates:
Because it targets two metabolic pathways, it may:
~20%
average weight loss at higher doses in the SURMOUNT-1 trial
In the SURMOUNT-1 trial (also published in the New England Journal of Medicine), participants achieved ~20% average weight loss at higher doses.
(See: Jastreboff et al., 2022)
Backlink reference: Jastreboff AM et al. "Tirzepatide Once Weekly for the Treatment of Obesity." NEJM. 2022.
| Feature | Wegovy | Mounjaro |
|---|---|---|
| Active ingredient | Semaglutide | Tirzepatide |
| Hormonal targets | GLP-1 | GLP-1 + GIP |
| Average weight loss | ~15% | ~20% |
| Injection frequency | Weekly | Weekly |
Individual response varies, and medication choice depends on:
For official prescribing information, see: UK regulatory guidance via the Medicines and Healthcare products Regulatory Agency GOV.UK
According to NICE and FDA guidance, these medications are generally prescribed for:
They are intended for chronic weight management.
Ref: Obesity management guidance from National Institute for Health and Care Excellence (NICE).
The most common side effects are gastrointestinal:
These usually improve during dose titration.
Rare but serious risks
| ⚠️ | Pancreatitis |
| ⚠️ | Gallbladder disease |
They are contraindicated in people with:
No.
The strongest outcomes in clinical trials occurred alongside:
| ✔ | Calorie control |
| ✔ | Increased protein intake |
| ✔ | Behavioural support |
| ✔ | Physical activity |
Long-term weight maintenance requires sustained lifestyle intervention.
The chronic disease model of obesity is supported by the World Health Organization, which recognises obesity as a complex metabolic condition requiring multi-factorial treatment. WHO
Rapid weight loss, regardless of method, can trigger:
This highlights the importance of nutritional monitoring during treatment.
How quickly do GLP-1 injections work?
Appetite suppression often begins within weeks. Clinically meaningful weight loss typically develops over 3-6 months.
Do you regain weight after stopping Mounjaro or Wegovy?
Data from extension studies suggest weight regain can occur if treatment and lifestyle support are discontinued.
Which causes more weight loss Mounjaro or Wegovy?
Clinical trial data suggests higher average reductions with Mounjaro, but individual variation is significant.
Are GLP-1 injections safe long-term?
Long-term cardiovascular outcome trials in diabetes populations suggest safety, but ongoing monitoring remains essential.
GLP-1 weight loss injections such as Wegovy (Semaglutide) and Mounjaro (Tirzepatide) represent a major advancement in obesity treatment.
They work by modifying appetite signalling and metabolic pathways, not by "boosting metabolism," but by helping regulate energy intake.
However, they are medical therapies, not lifestyle replacements.
The best outcomes occur when medication is combined with:
How Can TribElle Help?
We're not here to sell you a dream. We're here to back you up with:
Expert consultations with female-led clinicians who understand the mental and hormonal load.
Safe prescriptions with support every step of the way - including choosing between Wegovy and Mounjaro.
Ongoing check-ins, supplement guidance, and reorder options that don't make you jump through hoops.
And if you're still unsure? That's okay. Your body, your timeline.
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