28th May 2024

The Pros and Cons of Weight Loss Medications

Weight loss medications are making headlines in recent years, from celebrity-use speculations to explorations of whether they’re a cure-all solution to weight woes. Today, Dr Tanya Smith is exploring these tools to bring you the pros and cons of weight loss medications.

More than a quarter of adults in England are overweight or obese, and chronic disease and mortality rates are increasing as a result1. It’s therefore unsurprising that more and more options to support people in losing weight are being explored and brought to the public discourse. For some people who struggle to lose weight despite other interventions, doctors and patients may begin looking at medication as a way to support weight loss.

Sign up to our free email series here, featuring Dr Michael Mosley and a panel of health and medical experts, for all you need to know about weight loss medications. But to get you started, one of our medical advisors, Dr Tanya Smith, explains the pros and cons of weight loss medications and gives us insight into her own weight management journey with them.

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Dr Tanya’s Take on Weight Loss Medications

As a general practitioner with 35 years of experience and a special interest in weight management, I’ve seen my fair share of weight loss methods, both through lifestyle changes and pharmaceutical routes.

As with any medication, you must weigh up the pros and cons to see if it’s for you. This is no different with weight loss medications, and although I had my reservations at first as a doctor, it must be noted that I am actually in my first month of using Tirzepatide (Mounjaro) myself, and have lost 4% of my body weight. This is, of course, in addition to making lifestyle changes by following The Fast 800 Programme.
You may think that if you’re trying weight loss medication, it will be an easy solution. And, yes, the weight might fall off in the short-term if you use weight loss medications with no changes to your existing diet and lifestyle. For long-term success, however, you will get the most out of the weight loss medications when you pair them with a healthy lifestyle like The Fast 800 Programme.

What are weight loss medications?

What the media and the general population are referring to as “weight loss medications” of late are more often than not actually a class of drugs called GLP-1 Receptor Agonist Medications used to manage type 2 diabetes and obesity. They mimic the behaviour of the hormone GLP-1 that your body naturally creates when you eat food, making more insulin, reducing the amount of glucose your liver makes and slowing down digestion.

Exenatide (Byetta), liraglutide (Saxenda), semaglutide (Wegovy and Ozempic) and tirzepatide (Mounjaro) are all injectable medications that historically have been used for type 2 diabetes management. As a side effect, many patients lose weight while using these medications, and a number of these drugs have since been approved by medical regulatory bodies to be used as a treatment for obesity as the primary indication (although, the specific drugs approved for this do vary country to country).

Most weight loss medications work by reducing appetite and slowing digestion and gut motility, which gives a sense of fullness. They can also support a faster metabolism and decrease fat absorption, resulting in a typical 5-10% weight loss.2 Naturally, a reduced appetite typically results in fewer calories being consumed, too.

Pros of weight loss medications:

  • They are proven to produce weight loss results: It cannot be ignored that they have been shown to be effective for weight loss, particularly when paired with a healthy diet and lifestyle like The Fast 800. Studies have shown them to be a successful tool in achieving 15-20% body weight loss over 12 months, which is significant, but maintenance of this requires a sustainable diet and exercise routine.3
  • May result in other health benefits: Some weight loss medications have been shown to also have beneficial effects on blood sugar, blood pressure and cholesterol levels.4
  • May improve adherence to healthy eating plans: As weight loss medication can help control your appetite and increase satiety, they can complement and support a healthier diet, including the meal plans on The Fast 800 Programme.
  • Less invasive than weight loss surgery: If you’re struggling to lose weight through lifestyle and diet changes alone, medication is much less invasive than bariatric surgery, which is often a ‘last resort’ for people with obesity.
  • Approved by authorities for weight management: Many brands of weight loss medication have been approved for use by the FDA and NICE for use in the NHS as well as by Australia’s governing body, the TGA, which means that they are more regulated and will be more widely available.56

Cons of weight loss medications

  • When you stop, your appetite (and usually weight) returns: These drugs suppress hunger, which may be useful for people who frequently over eat or find themselves snacking. However, because you may not be able to stomach the quantity of calories you previously could, it’s so important to prioritise the quality of those calories to avoid malnutrition. For long-term weight loss, even after medication is stopped, a sustainable and health-promoting diet like a Mediterranean-style diet should be followed during and after weight loss medication use.
  • Loss of lean body mass: More studies are required to discover an accurate percentage of lean body mass that is lost while on weight loss medications, but it seems to be around 30-40% with Wegovy and 10% with Mounjaro. When you lose weight very quickly, it’s expected you will lose muscle mass, especially if your diet is lacking in protein and you are not doing any resistance training, which supports muscle maintenance. Making sure resistance exercise is part of your lifestyle can help to maintain lean body mass. There’s plenty of great workout videos on The Fast 800 Programme if you need help with getting started with resistance training.
  • Supply issues and cost: There are ongoing supply issues of particular drugs, where supply cannot meet demand, so you may be prescribed an alternative should your doctor assess you as a good candidate for weight loss medications. Moreover, if your reasons for using these medications are not approved as a primary indication (by NICE in the UK, and TGA in Australia), your doctor may not be able to prescribe particular medications for weight loss alone. Most people looking to use weight loss medications who don’t meet the medical criteria to have these drugs subsidised will be funding their prescription privately. This can set you back over £150 a month in the UK and $300+ in Australia.
  • Common side effects can affect quality of life for the duration of taking these medications: Nausea, vomiting, diarrhoea, headaches, constipation, bloating, flatulence, dizziness and fatigue are all common side effects of using weight loss medication.
  • Like any medication, there are potential risks of serious side effects: Pancreatitis, gallstones, thyroid cancer, low blood sugar in diabetics, deterioration in vision in diabetics, kidney failure, increased heart rate, serious allergic reactions, depression and suicidal thoughts are less common but still associated as a risk with some medications.
  • Contraindications: Many weight loss medications are not suitable for pregnant or breast-feeding people, those with a history of certain cancers, those with gastrointestinal conditions like inflammatory bowel disease, diabetic retinopathy and mood disorders. It’s imperative to talk to a health professional before using these drugs.

How The Fast 800 helps Dr Tanya’s weight loss medication journey

With rapid weight loss and a significant reduction in appetite, weight loss medications may put you at risk of losing critical lean muscle mass, and even malnutrition, if not used in conjunction with an appropriate diet and exercise. It’s therefore essential to ensure you’re getting in enough protein, fibre and healthy fats every day. Planning your nutrition is easy with The Fast 800 Programme and while on my own medication journey it’s been invaluable for me to have meals and workouts laid out for me each week. With fasting days sitting around the 800-calorie mark, and with an emphasis on protein and fibre, they are well-suited to someone like me who has a reduced appetite while using medication as a weight loss tool.

Furthermore, The Fast 800 members are well equipped to continue their healthy lifestyle once they’ve reached their goal, which is important for long-term success. So, my plan is to continue with the medication until I get to a healthier BMI and then stop, before moving onto the Way of Life approach on The Fast 800 Programme. Sticking to a Mediterranean-style diet and keeping up with resistance training will ensure I am able to maintain results and lean mass better, and I know I can then fall back on The New 5:2™ approach if I begin to gain weight again.

All in all, although there are pros and cons of weight loss medications, they are not a fix-all solution: diet and lifestyle changes are still necessary for longer term success.

Sign up to The Fast 800’s free email series about weight loss medication now to learn more.


Tchang BG, Aras M, Kumar RB, et al. Pharmacologic Treatment of Overweight and Obesity in Adults. [Updated 2021 Aug 2]. In: Feingold KR, Anawalt B, Blackman MR, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279038/

Jastreboff, A, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med, July 2022; 387:205-216, DOI: 10.1056/NEJMoa2206038.

Siebenhofer A, Winterholer S, Jeitler K, Horvath K, Berghold A, Krenn C, Semlitsch T. Long-term effects of weight-reducing drugs in people with hypertension. Cochrane Database Syst Rev. 2021 Jan 17;1(1):CD007654. doi: 10.1002/14651858.CD007654.pub5. PMID: 33454957; PMCID: PMC8094237.

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