Prescription weight-loss injections: Who are they for and how do they work?
Doctors from Bay Medical Clinic explain when weight-loss injections may be prescribed for obesity, what patients should consider and why lifestyle changes remain essential for long-term results
During a consultation, doctors assess each patient’s overall health and individual needs before recommending an appropriate weight management approach
PHOTO: BAY MEDICAL CLINIC
Obesity is more complex than simply eating too much or exercising too little. According to Dr Bernard Tan, medical director at Bay Medical Clinic, it is influenced by a combination of factors, including hormones that regulate appetite and metabolism, genetics, sleep, stress, lifestyle habits and underlying medical conditions.
Reflecting this complexity, the World Health Organization (WHO) recognises obesity as a chronic disease rather than simply a lifestyle issue.
“This is why some people struggle to lose weight,” explains Dr Tan.
Left untreated, obesity and excess weight can also raise the risk of developing a range of chronic health conditions, including Type 2 diabetes, high blood pressure, heart disease and fatty liver disease, says Dr Tan
“Obesity is also linked to conditions such as obstructive sleep apnoea and joint problems, which can affect quality of life.”
According to the National Population Health Survey, the proportion of Singapore residents living with obesity increased from 10.5 per cent in the 2019 to 2020 survey to 12.7 per cent in the 2023 to 2024 survey.
Healthy eating, regular exercise and sustainable lifestyle changes remain the cornerstone of long-term weight management, says Tan.
But for some people living with obesity, lifestyle measures alone may not be enough. In such cases, doctors may consider prescription medicines, including injectable GLP-1-based therapies, as part of a comprehensive weight management programme
How do prescription weight-loss injections work?
According to Dr Tan, GLP-1, which stands for glucagon-like peptide-1, is a hormone naturally produced by the gut after a meal to signal to the brain that a person is full. It also prompts the pancreas to release insulin, helps regulate blood sugar, slows stomach emptying and reduces food cravings
Another hormone, GIP (glucose-dependent insulinotropic polypeptide), also stimulates insulin release but plays a different role in how the body uses and stores energy
Tirzepatide is a class of prescription medication that mimics the actions of both GLP-1 and GIP. By activating both pathways, it helps regulate appetite, improve blood sugar control and support weight loss when used alongside lifestyle changes.
“Many prescription weight-loss medicines work by acting on the GLP-1 pathway alone,” notes Dr Tan. “Tirzepatide, however, works differently. It is a dual GIP and GLP-1 receptor agonist – meaning it activates the receptors for both hormones, mimicking their natural effects in the body.”
Adds Dr Hoe Ying Min, medical director at Bay Medical Clinic: “By doing so, it leads to reduced appetite, increased feelings of fullness, fewer cravings and a lower overall calorie intake. A medical weight loss programme aims for a sustained caloric deficit over a period to achieve long-term, sustainable weight loss.”
Dr Hoe cites the Surmount-5 trial, a 72-week study involving 751 adults living with obesity that evaluated tirzepatide
The study, published in the New England Journal of Medicine in May 2025, found that participants receiving tirzepatide lost, on average, about 20 per cent of their body weight over the course of the study.She adds: “In addition to weight loss, the Surmount-1 trial also reported improvements in certain health measures, including blood sugar, blood pressure and cholesterol, in some patients receiving once-weekly tirzepatide. Individual responses to treatment may vary.”However, medication alone is not a silver bullet for obesity as weight gain will eventually happen after treatment stops, says Dr Hoe.
“In the Surmount-4 trial, patients who were treated with tirzepatide for nine months subsequently stopped treatment for a year. On average, they regained about half the weight they had lost.”
She stresses: “Obesity is a chronic condition requiring long-term follow-up; the initial treatment with weight-loss injections need to be followed by lifestyle changes.”
Dr Tan advises obese patients to first lose some excess weight before they are able to exercise meaningfully, by climbing stairs, going for a run and so on. “For some patients, prescription medication may support initial weight loss, making it easier to adopt sustainable lifestyle changes under medical supervision.”
Are prescription weight-loss injections right for you?
According to Dr Tan, such medicines are not intended for individuals of normal weight who want to shed a few kilos
He says prescription weight-loss injections are clinically indicated for adults with obesity (a body mass index, or BMI, of 30kg/m² or higher), or those who are overweight (a BMI of 27kg/m² to 30kg/m²) and have obesity-related conditions such as high cholesterol, Type 2 diabetes and obstructive sleep apnoea, following a doctor’s assessment
According to the WHO’s conditional recommendations, GLP-1 therapies are prohibited for children and adolescents below the age of 21, and there is no safety data for pregnant and breastfeeding women
Most patients experience mild-to-moderate gastrointestinal side effects – such as nausea, diarrhoea, constipation and bloating – especially during the initial one to two months during the dose escalation period, notes Dr Tan
“In rare cases, patients may develop gallstones or inflammation of the gallbladder or pancreas due to the gallstones. These patients will experience severe abdominal pain and vomiting and will need to go to a hospital’s accident and emergency department immediately. This affects less than 1 per cent of patients.”
Cautions Dr Hoe: “Prescription weight-loss injections should be obtained only through registered healthcare professionals at licensed clinics. Patients should avoid buying medications from online sellers, friends, overseas agents or unverified
For those who do not require medical treatment, Dr Tan recommends focusing on sustainable lifestyle habits instead of drastic diets.
He advises: “Try eating until you’re about 80 per cent full, cut back on sugary drinks and late-night suppers, and remember that every bit of physical activity counts – whether it’s taking the stairs, going for a walk or doing household chores.
“Having a partner or friend to keep you accountable can also make the journey easier. Most importantly, aim for habits you can maintain over the long term rather than striving for perfection.”
Find out more aboutBay Medical Clinic’s doctor-supervised medical weight management programmes
Disclaimer: This article is for educational purposes only and is not medical advice. Individuals are recommended to consult with their doctor for appropriate treatment
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