Weight Loss Injections Explained: Semaglutide, Tirzepatide & Retatrutide

A modern tool for fat loss, metabolic health, and physique optimisation

Weight-loss medications like semaglutide and tirzepatide have completely changed the landscape of metabolic health. What started as diabetes drugs are now some of the most powerful tools we have for reducing body fat, improving insulin sensitivity, and lowering long-term disease risk.

They’re also increasingly being used by fit, health-conscious men — including gym-goers — to support cutting phases, appetite control, and body recomposition.

Why body fat still matters (even if you train hard)

You can lift heavy, train consistently, and still carry excess visceral fat. That matters because body fat — particularly around the organs — is linked to:

• Insulin resistance

• Cardiovascular disease

• Fatty liver

• Lower testosterone

• Chronic inflammation and accelerated ageing

Reducing fat mass while preserving muscle is one of the most powerful levers for healthspan and longevity.

Semaglutide (Ozempic / Wegovy)

Class: GLP-1 receptor agonist

How it works

Semaglutide mimics GLP-1, a gut hormone that:

• Reduces appetite and food noise

• Slows gastric emptying

• Improves insulin sensitivity

• Reduces cravings and impulsive eating

Typical prescribing indications

• Type 2 diabetes

• Chronic weight management in people with:

  
  

  • BMI ≥30, or

  • BMI ≥27 with metabolic risk factors

  
  

What people see

• Average fat loss: 10–15% of body weight

• Marked reduction in waist circumference

• Improved glycaemic control and cardiometabolic markers

Side effects are usually dose-related and manageable when titrated properly.

Tirzepatide (Mounjaro / Zepbound)

Class: Dual GIP + GLP-1 receptor agonist

Tirzepatide works on two hormonal pathways, which is why results tend to be stronger.

Why it stands out

• Greater appetite suppression

• Better insulin sensitivity

• More consistent fat loss

Typical prescribing indications

• Type 2 diabetes

• Weight management (depending on regulatory approval)

Expected outcomes

• 15–22% body weight reduction in trials

• Significant visceral fat loss

• Often superior to semaglutide in head-to-head studies

For many people, this is currently the most effective approved option.

Retatrutide – where things are heading

Class: Triple agonist (GLP-1, GIP, glucagon receptor)

Retatrutide represents the next generation of metabolic drugs.

Why there’s so much interest

• Early trials show >24% average weight loss

• Improvements in energy expenditure

• Better fat-to-lean mass ratios (still being studied)

Important context

Retatrutide is not yet approved and remains investigational. While the early data is exciting, long-term safety and optimal use are still being defined.

A realistic conversation for gym-focused men

Plenty of motivated, disciplined men — including those already lean — are using GLP-1–based medications as tools, not shortcuts.

These drugs:

• Make calorie control easier

• Reduce food noise during cuts

• Improve metabolic efficiency

• Can support sharper, more sustainable fat loss

When used well, they can complement training and nutrition — not replace them.

The key is optimisation, not suppression

The goal isn’t to eat as little as possible. It’s to:

• Lose fat

• Preserve muscle

• Maintain performance

• Protect hormones and recovery

That means using the lowest effective dose, matching intake to training demands, and keeping the long game in mind.

Smart principles if this is part of your strategy

• Keep protein intake high (>1.6-2.2g/kg)

• Continue progressive resistance training

• Avoid racing doses upward

• Monitor strength, energy, sleep, and mood — not just the scale

• Support hydration and electrolytes

• Adjust calories intentionally, not accidentally

When these drugs are integrated thoughtfully, they can be powerful allies for both health and physique.

While emerging therapies and off-label use are an active area of discussion, my role as a doctor is to prioritise evidence, safety, and long-term outcomes above all else.

What these medications are (and aren’t)

They are:

• Legitimate medical tools with strong evidence

• Highly effective for fat loss and metabolic health

• Compatible with serious training when used correctly

They are not:

• A replacement for lifting, sleep, or protein

• Something to “wing” without understanding your body

• One-size-fits-all

The bottom line

GLP-1–based medications are one of the biggest advances in metabolic and preventative medicine we’ve seen.

Used appropriately, they can:

• Improve body composition

• Reduce long-term disease risk

• Support longevity and aesthetics

Whether your goal is better health, better bloods, or a leaner, sharper physique — the conversation should be individualised, evidence-based, and non-judgemental.