Side Effects, including Unintended Side Effects of GLP-1 Weight Loss Medications
Weight loss medications have become an increasingly popular option for people struggling with obesity. In previous articles, our Surry Hills doctors wrote about:
- Injectable Weight Loss Medications and New Oral GLP-1 Medications: a 2026 Updates (a Surry Hills doctors Guide)
- Injectable Weight Loss Medications Part 2: Wegovy vs Ozempic – Which Medication Is Better? (A Surry Hills GP Guide)
Whilst GLP-1 analogues have helped many Australians achieve significant weight loss when combined with healthy lifestyle changes, it is important to understand the potential side effects and how to maintain your health throughout treatment.
At Crown St Medical Centre – Surry Hill medical practice, we aim to help Surry Hills patients understand the benefits, risks, and long-term considerations of weight loss medications.
What Are GLP-1 Weight Loss Medications?
GLP-1 (Glucagon-Like Peptide-1) medications work by mimicking a natural hormone that helps regulate appetite, slow stomach emptying, and increase feelings of fullness. This can lead to reduced calorie intake and significant weight loss.
Common GLP-1 medications prescribed in Australia include:
- Ozempic and Wegovy (Semaglutide)
- Mounjaro (Tirzepatide)
- Saxenda (Liraglutide)
These medications can be highly effective, but like all treatments, they may cause unwanted side effects and require ongoing monitoring.
Common Side Effects of GLP-1 Weight Loss Medications
Many patients experience mild side effects when starting treatment or increasing their dose. These commonly include:
- Nausea, Vomiting, Diarrhoea, Constipation
- Bloating, Indigestion, Reduced appetite and Fatigue
For most people, these symptoms improve over time as the body adjusts to the medication.
Less Common but Important Side Effects
Although uncommon, some patients may experience:
- Gallstones
- Pancreatitis
- Worsening reflux symptoms
- Loss of lean body mass
- Improved Fertility in Females
This last 2 points are becoming an important topic in obesity medicine and deserves special attention.
Loss of Lean Body Mass – Can GLP-1 Medications Cause Muscle Loss?
While GLP-1 agonists do not directly breakdown muscle tissue. GLP-1 medications are designed to reduce body fat, some of the weight loss can also come from lean muscle tissue. The main hypothesis for muscle loss are:
- Reduced Physical Activity: Lower energy levels can reduce resistance training exercises need for muscle building.
- Low Calorie Intake: When GLP-1 agonists suppress appetite and caloric intake is too low, the body will break down both fat and muscle for energy requirements.
- Reduced Consumption of Protein: Smaller meals are often associated with a reduction in protein intake. Without adequate dietary protein and amino acids, the body cannot produce and repair muscle.
- Rapid Weight Loss: Rapid weight loss can result in the body shedding lean muscle and fat.
Research suggests that a proportion of weight lost with GLP-1 medications may be lean body mass if preventative strategies are not implemented.
Maintaining muscle is important because muscle tissue:
- Supports metabolism
- Improves strength and mobility
- Reduces injury risk
- Helps maintain long-term weight loss
- Supports healthy ageing
For this reason, preserving muscle bulk should be a key goal during any medically supervised weight loss program.
How to Maintain Muscle Bulk While Using GLP-1 Medications
- Prioritise Protein Intake
Protein provides the building blocks needed to preserve muscle tissue during weight loss.
Good protein sources include:
- Lean meats
- Fish
- Eggs
- Greek yoghurt
- Tofu
- Legumes
- Protein supplements when appropriate
Many patients on GLP-1 medications eat substantially less food overall, making protein intake even more important.
- Perform Resistance Training
Strength training is one of the most effective ways to maintain muscle mass during weight loss.
Examples include:
- Weight training
- Resistance bands
- Pilates
- Bodyweight exercises
- Functional strength programs
Even two to three resistance training sessions per week can make a significant difference.
- Avoid Excessively Rapid Weight Loss
Although dramatic weight loss may seem appealing, losing weight too quickly can increase muscle loss.
A medically supervised program helps ensure weight loss occurs at an appropriate rate while supporting long-term success.
- Monitor Body Composition
The number on the scales does not tell the whole story.
Monitoring:
- Fat mass
- Muscle mass
- Waist circumference
- Strength levels
can provide a more accurate picture of progress.
- Regular Medical Review
Regular follow-up appointments allow treatment plans to be adjusted and nutritional requirements reviewed throughout the weight loss journey.
Improved Fertility in Females
How Do GLP-1 Medications Improve Fertility?
With weight loss and improved metabolic health, female reproductive function may be enhanced through several pathways:
- Weight-Related Ovulation: Excess weight and obesity can disrupt the menstrual cycle. Losing 5-10% of body weight can rebalance hormones and trigger the resumption of regular ovulation.
- Reversing Polycystic Ovarian Syndrome (PCOS): Polycystic Ovary Syndrome (PCOS) has now been renamed Polyendocine Metabolic Ovarian Syndrome. It is a leading cause of infertility driven by insulin resistance and high testosterone. GLP-1s lower blood insulin levels, which in turn decreases excess testosterone. This helps reverse polycystic ovary changes and encourages regular periods. Losing weight can also rebalance hormones and improves insulin resistance.
- Direct Hormonal and Brain Effects: Early research suggests GLP-1s might also act directly on the brain’s hypothalamus to stimulate the release of gonadotropin-releasing hormone (GnRH). This kickstarts the communication between the brain and the ovaries, promoting healthy follicle growth.
- Decreased Inflammation: GLP-1s are found to have an anti-inflammatory effects throughout the body, including on the ovaries and the uterine lining. The theory is that this can support embryo implantation.
Important Considerations:
- Birth Control Interference: Another way GLP-1 medications act is to delay gastric emptying. This can interfere with the absorption of the oral contraceptive pills resulting in unintended pregnancies. This phenomenon often referred to as “Ozempic babies”.
- Pregnancy Safety: GLP-1s are not recommended during pregnancy. If you are actively trying to conceive, doctors typically advise stopping these medications one to two months beforehand to ensure they are fully cleared from your system
Are GLP-1 Medications Right for Everyone?
Not necessarily. Some patients may not tolerate the side effects, while others may have medical conditions that make alternative approaches more suitable. Our Surry Hills GPs can provide a personalised assessment and discuss whether GLP-1s are right for you.
At Crown St Medical – Surry Hill’s local Medical Practice, we work with patients to develop individualised weight management plans that may include lifestyle interventions, medication, nutrition support, and ongoing monitoring.
Our physiotherapist, Peter can help with a tailored exercise program to assist you with your weight management journey.
Want to Know More About Different Treatments?
While GLP-1 medications receive significant attention, they are not the only prescription weight loss treatments available in Australia.
Contrave®
Contrave is a prescription medication that combines two active ingredients:
- Naltrexone
- Bupropion
Together, they act on areas of the brain involved in appetite regulation, cravings, and reward pathways. This may help reduce food cravings and support healthier eating behaviours.
Contrave may be suitable for some patients who are not candidates for GLP-1 medications or who prefer an alternative treatment approach.
Stay tuned for our upcoming article: “Alternative Weight Loss Medications Available in Australia”, where we explore Contrave and other treatment options in greater detail.
Frequently Asked Questions About GLP-1 Weight Loss Medications
Do GLP-1 medications really work for weight loss?
Yes. Clinical studies and real-world experience show that GLP-1 medications can help many patients achieve meaningful weight loss when combined with dietary and lifestyle changes.
How much weight can you lose on GLP-1 medications?
Results vary between individuals. Factors such as starting weight, lifestyle habits, medication adherence, and underlying health conditions all influence outcomes.
Is muscle loss inevitable with GLP-1 medications?
No. While some muscle loss can occur during any weight loss program, adequate protein intake, resistance training, and appropriate medical supervision can help preserve muscle mass.
What foods should I eat while taking GLP-1 medications?
A balanced diet focused on Lean protein, Vegetables, Whole grains and Healthy fats can help support weight loss while maintaining muscle and overall health.
What happens if I stop taking GLP-1 medication?
Some patients regain weight after stopping treatment, particularly if lifestyle changes have not been maintained. Long-term weight management strategies are therefore important.
Can I get weight loss medication from Crown St Medical Centre Doctors in Surry Hills?
Crown St Medical Centre doctors provides comprehensive assessments for patients seeking medical support for weight management. Treatment recommendations are based on your medical history, health goals, and suitability for available therapies. Dr Thao Nguyen and most of our Surry Hills Doctors team can assist where you are deemed suitable. Please note, some doctors do not prescribe GLP-1 medications. It is best to discuss with your regular GP or check with our reception team if you are unsure.
Book a Consultation with our Surry Hills doctors and GPs
If you’re considering GLP-1 weight loss medications, have concerns about side effects, or want advice on preserving muscle mass during weight loss, the team at Crown St Medical – Surry Hills Medical Centre can help.
Our experienced doctors provide evidence-based weight management consultations tailored to your individual health needs, helping you achieve sustainable results while protecting your long-term health and wellbeing.
Last medically reviewed: 31 May 2026
Reviewed by: Doctors at Crown St Medical Centre – Surry Hills doctors
Location: Crown Street, Surry Hills NSW
