Weight Loss Medications Explained: How Semaglutide, Liraglutide and Orlistat Work

1. Introduction

The global weight management market has grown significantly in recent years, reflecting the rising prevalence of overweight and obesity worldwide. As more individuals seek effective ways to manage their weight, there is increasing interest in medical treatments that can support lifestyle changes such as diet and exercise.

While weight loss was traditionally viewed as a matter of willpower, research now shows that body weight is influenced by a complex interaction of genetics, hormones, metabolism, appetite regulation and environmental factors. More than 400 genes have been associated with body weight regulation, helping to explain why weight loss can be more difficult for some individuals than others.

Today, medications such as semaglutide, liraglutide and orlistat are increasingly used as part of weight management strategies. Although they all support weight loss, they work through very different biological pathways.

2. How the Body Regulates Weight

Weight regulation is determined by the balance between energy intake, energy expenditure and fat absorption.

Energy intake refers to calories consumed from food, while energy expenditure refers to calories used through metabolism and physical activity. A third factor, fat absorption, determines how much dietary fat is ultimately taken up by the body.

Most weight loss medications work by influencing one or more of these pathways in order to reduce overall calorie balance and support weight reduction.

3. Appetite Regulation and Metabolic Control

Appetite is regulated by a complex system of hormonal signals between the digestive system and the brain. Two key hormones involved are ghrelin and leptin:

• Ghrelin stimulates appetite and increases hunger signals

• Leptin promotes satiety and helps reduce food intake

When these signals become imbalanced, individuals may experience increased hunger, stronger cravings and difficulty controlling food intake.

Metabolism also plays an important role in weight regulation. The body continuously converts food into energy and determines whether excess energy is stored as fat or used for fuel. Hormones such as insulin, glucagon and adrenaline help regulate this balance, influencing whether the body is in a fat-storing or fat-burning state.

4. GLP-1 Receptor Agonists: Semaglutide and Liraglutide

Semaglutide and liraglutide belong to a class of medications known as GLP-1 receptor agonists. GLP-1 is a naturally occurring hormone that helps regulate appetite, blood sugar levels and digestion. These medications work by mimicking the action of this hormone in the body.

They support weight loss through several complementary effects:

• Enhancing insulin secretion when needed

• Reducing glucagon levels

• Slowing gastric emptying

• Improving glycaemic control

• Acting on appetite centres in the brain to reduce hunger and increase satiety

By influencing both appetite regulation and metabolic pathways, GLP-1 receptor agonists help individuals feel fuller sooner and remain satisfied for longer, which may lead to reduced calorie intake over time.

While both medications are effective, they differ mainly in dosing frequency:

• Semaglutide is typically administered once weekly

• Liraglutide is administered once daily

Clinical evidence generally shows greater average weight loss with semaglutide compared to liraglutide, although both remain effective when used appropriately.

Common side effects include gastrointestinal symptoms such as nausea, vomiting, diarrhoea, constipation and abdominal discomfort, particularly during dose escalation.

5. Orlistat: Reducing Fat Absorption in the Gut

Orlistat works through a completely different mechanism compared to GLP-1 receptor agonists. Instead of acting on appetite or hormonal pathways, it works locally in the digestive system.

It inhibits pancreatic lipase, an enzyme responsible for breaking down dietary fat. As a result, a portion of the fat consumed in meals is not absorbed and is instead excreted from the body. This reduces overall calorie intake and can contribute to gradual weight loss over time.

As it does not act on appetite regulation, orlistat does not directly influence hunger or satiety signals.

Its effectiveness is closely linked to dietary habits. Individuals consuming higher-fat meals are more likely to experience gastrointestinal side effects, which may include:

• Oily or fatty stools

• Flatulence with discharge

• Increased bowel urgency

• Loose stools

• Abdominal discomfort

To minimise these effects, individuals are generally advised to moderate dietary fat intake as part of treatment.

6. Comparing Semaglutide, Liraglutide and Orlistat

In general, GLP-1 receptor agonists work by influencing appetite and metabolic control, while orlistat reduces calorie intake by limiting fat absorption in the gut.

7. Long-Term Considerations in Weight Management

Weight loss is often followed by biological adaptations that can make long-term maintenance challenging. When weight is reduced, the body may lower energy expenditure and increase hunger signals, which can promote regaining of weight.

These responses are part of the body’s natural regulatory system and help explain why sustained weight management is often difficult with lifestyle measures alone.

For this reason, obesity is increasingly recognised as a chronic condition that may require long-term management strategies.

GLP-1 receptor agonists such as semaglutide and liraglutide may help address both appetite regulation and metabolic adaptation. However, medication should not be viewed as a standalone solution.

Long-term success still depends on consistent lifestyle habits, including balanced nutrition, regular physical activity, resistance training, adequate protein intake and ongoing behavioural changes.

8. How Pharmacists Can Support Weight Management

With a growing range of weight management options available, selecting the most appropriate approach can sometimes feel overwhelming. Pharmacists play an important role in helping individuals navigate these options safely and effectively.

Through personalised consultations, pharmacists assess health status, lifestyle factors and treatment goals to provide suitable recommendations. This may include guidance on medications, supplements and lifestyle strategies, as well as support in managing side effects and improving adherence.

Ongoing pharmacist support can also help individuals build sustainable habits and monitor progress over time, improving the likelihood of long-term success.

At Glovida Pharmacy, pharmacist-led weight management consultations are available to support individuals throughout their journey. For personalised advice, individuals may complete a weight management questionnaire or contact the pharmacy team via WhatsApp at 8101 5555.