27 is the Magic Number: Why a BMI of 27 or Over Is the Cut-Off for Weight Loss Medications

With obesity rates continuing to rise across the UK, more people are turning to clinically proven weight-loss treatments to help manage their health. Among the most popular and effective options are weight-loss injections like Mounjaro (tirzepatide), Wegovy (semaglutide), and Orlistat (a lipase inhibitor). However, access to these treatments isn’t open to everyone – there’s a key eligibility criterion that must be met: a Body Mass Index (BMI) of 27 or higher.

But why is 27 the magic number? In this in-depth blog, we explain the science and reasoning behind this threshold, the medical significance of a BMI ≥27, and how you can safely access regulated weight-loss treatments through Happy Pharmacy.

What Is BMI and How Is It Calculated?

BMI (Body Mass Index) is a simple measurement used by healthcare professionals to assess whether a person’s weight is within a healthy range relative to their height. The formula is:

BMI = weight (kg) / height (m²)

BMI categories are:

• Underweight: <18.5

• Normal weight: 18.5–24.9

• Overweight: 25–29.9

• Obese: 30 and above

So, a BMI of 27 falls into the “overweight” category – but not yet into the “obese” range. It’s in this category that weight-related health risks begin to increase, which is why it’s often the cut-off for weight-loss medications under medical supervision.

Why Is BMI ≥27 the Cut-Off for Weight Loss Injections?

The decision to set BMI 27 as a threshold is based on clinical evidence, health risk data, and medicines regulatory guidance. Here’s why this number matters:

1. Increased Health Risks Begin at BMI 27

Studies show that individuals with a BMI of 27 or above begin to face increased risks of:

• Type 2 diabetes

• High blood pressure

• Sleep apnoea

• Joint pain and arthritis

• Cardiovascular disease

This risk increases further with additional weight, but the early intervention at this stage can prevent progression to obesity and more serious complications. This is where weight-loss injections like Wegovy, Mounjaro, and Orlistat come into play.

2. Clinical Trials Use BMI 27 as Inclusion Criteria

Both Mounjaro (tirzepatide) and Wegovy (semaglutide) were tested in large clinical trials involving individuals with a BMI of 27 or higher – particularly those who also had at least one weight-related condition, such as hypertension or pre-diabetes.

These trials demonstrated significant, sustained weight loss, leading to regulatory approval for patients meeting this criterion. The data supports the efficacy and safety of these medications in this group.

3. NICE and MHRA Guidelines Reflect This Standard

In the UK, guidance from NICE (National Institute for Health and Care Excellence) and oversight from the MHRA (Medicines and Healthcare products Regulatory Agency) stipulate that certain weight-loss treatments can be prescribed for:

• Adults with BMI ≥30, or

• Adults with BMI ≥27 and at least one weight-related comorbidity.

This ensures a regulated, clinically appropriate use of medications like Mounjaro, Wegovy, and Orlistat.

Understanding the Treatments: Mounjaro, Wegovy, and Orlistat

Let’s break down how each medication works and their role in medically assisted weight loss.

Mounjaro (tirzepatide)

• Mechanism: Dual GIP and GLP-1 receptor agonist

• Effect: Suppresses appetite, delays gastric emptying, improves blood sugar control

• Use: Weekly injection

• Eligibility: BMI ≥30 or BMI ≥27 with comorbidities

• Benefits: Average weight loss of up to 20% in clinical trials

Wegovy (semaglutide)

• Mechanism: GLP-1 receptor agonist

• Effect: Reduces hunger, increases satiety, supports long-term weight loss

• Use: Weekly injection

• Eligibility: Same as Mounjaro

• Benefits: Average weight loss of 15% over 68 weeks in studies

Orlistat (Alli, Xenical)

• Mechanism: Lipase inhibitor that reduces fat absorption in the gut

• Effect: Blocks ~30% of fat calories from being digested

• Use: Oral capsule taken with meals

• Eligibility: BMI ≥28

• Benefits: Less potent than injections but helpful for mild-to-moderate weight loss

Each treatment is available via Happy Pharmacy following a thorough online consultation to ensure it’s safe, appropriate, and regulated for your health profile.

What Happens If My BMI Is Under 27?

If your BMI is below 27, weight-loss injections are not typically recommended – unless you have a rare medical condition and are under specialist care.

Why not?

• The risks may outweigh the benefits at this stage.

• There is limited data on the efficacy of these drugs in normal-weight individuals.

• Regulatory guidance prohibits off-label use in people below the eligibility threshold.

Happy Pharmacy adheres strictly to MHRA regulations, ensuring that all treatments are prescribed safely and ethically.

Benefits of Early Intervention at BMI 27+

Tackling weight gain when your BMI is between 27 and 30 has several key advantages:

• Prevents progression to obesity

• Reduces the risk of chronic disease

• Improves mobility and mental health

• Enhances self-confidence and energy levels

By starting treatment at this stage, patients often achieve better long-term outcomes – and medications like Wegovy, Mounjaro, and Orlistat offer powerful tools for success.

A Word on Safety and Regulation

Unfortunately, the rising demand for weight-loss injections has led to a surge in unregulated online sellers, many offering counterfeit or unsafe versions of these medications.

This can pose serious health risks.

When you choose Happy Pharmacy, you are guaranteed:

• MHRA-approved treatments

• Prescriptions issued by UK-registered healthcare professionals

• Secure, discreet delivery

• Ongoing clinical support

• Transparent pricing and trusted advice

We are a fully regulated online pharmacy, committed to providing safe and effective weight-loss solutions to UK patients.

Is BMI a Perfect Measurement?

While BMI is a useful population-level tool, it has some limitations:

• It doesn’t differentiate between muscle and fat mass

• It may not reflect body fat distribution

• It may be less accurate in certain ethnic groups

That said, it remains a clinically accepted standard for determining eligibility for treatment. Your prescriber at Happy Pharmacy will also consider your medical history, lifestyle, and health goals in conjunction with your BMI.

How to Check Your BMI and Get Started

You can calculate your BMI at home using a reliable BMI calculator (available on the NHS website or directly through Happy Pharmacy’s consultation form).

If your BMI is:

• 27–29.9: You may qualify for Wegovy, Mounjaro, or Orlistat if you have a weight-related condition.

• 30 or above: You likely qualify for all major weight-loss treatments, including injectables.

Next steps:

1. Complete our secure online consultation

2. Receive eligibility confirmation from a licensed prescriber

3. Order your medication for discreet home delivery

4. Track your progress with the support of Happy Pharmacy

Final Thoughts: Why 27 Is More Than Just a Number

A BMI of 27 or more represents a critical turning point – a stage where early intervention can dramatically improve your health trajectory. Thanks to regulated, clinically proven options like Mounjaro, Wegovy, and Orlistat, individuals in this category have real tools to achieve lasting weight loss safely.

At Happy Pharmacy, we are proud to offer compassionate, expert-led care for people navigating their weight-loss journey. Whether you’re just reaching a BMI of 27 or have struggled with your weight for years, we’re here to help you find a path that’s safe, sustainable, and supported by science.

Blog medically reviewed by : Nigel Howard, GPhC Registered Prescriber, 27 May 2025

References

1. NHS. Body Mass Index (BMI) Calculator and Classification. 
2. National Institute for Health and Care Excellence (NICE). Obesity: Identification, Assessment and Management. 
3. Medicines and Healthcare products Regulatory Agency (GPHC). Safe Online Pharmacies and Weight-Loss Medications. 
4. SURMOUNT-1 Trial. New England Journal of Medicine, 2022 – Tirzepatide (Mounjaro).
5. STEP Trials. Novo Nordisk Clinical Studies on Semaglutide (Wegovy).
6. NICE Guidance: Orlistat for Obesity in Adults.
7. British Dietetic Association – Obesity and Weight Management Guidelines.