The quest to combat obesity has led to the development of groundbreaking medications like Mounjaro (tirzepatide), often dubbed the "King Kong" of weight loss drugs, and other GLP-1 receptor agonists like Ozempic (semaglutide). While these drugs offer promising results, understanding their mechanisms, efficacy, and potential side effects is crucial for informed decision-making.
What is Mounjaro?
Mounjaro is an injectable prescription medicine that improves and lowers blood sugar levels in adults with type 2 diabetes. As of June 2025, people with obesity can gain access to Mounjaro via their GP services in England. This drug works by activating two receptors (GLP-1 and GIP) to increase the level of hormones in the body, according to Diabetes.org. Not only does it help your body to produce more insulin and lower your blood sugar levels, but it slows down how quickly food is digested - making it a popular weight-loss solution.
How Mounjaro Works
Mounjaro, containing the active ingredient tirzepatide, uniquely activates two hormones: glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). GLP-1 agonists mimic natural hormones in the body, promoting a sensation of fullness and slowing down digestion. This leads to better blood sugar control and weight loss. GIP complements this action, further enhancing insulin secretion and potentially contributing to greater weight loss. This combination of effects makes Mounjaro a compelling option for those seeking to manage their weight effectively.
Mounjaro Dosage and Administration
Those on Mounjaro are advised to inject the drug under the skin once per week. This can either be in your thigh, your upper arm, or in your stomach, Boots’ Online Doctor reports. It’s important that you follow dosage instructions strictly. Usually, these doses increase every four weeks until you reach a maximum maintenance dose of either 5mg, 10mg, or 15mg. According to Boots, Mounjaro should start working right away. But be warned: it could take several weeks before you notice an improvement where your blood sugar level is concerned.
Retatrutide: A New Player in Weight Loss
In the constant quest to combat obesity and its associated health risks, a groundbreaking development has emerged - a new weight loss injection named "retatrutide". What sets retatrutide apart is its innovative mechanism of action, targeting three distinct receptors in the brain. Unlike existing weight loss jab, retatrutide goes a step further by turbocharging calorie burning while simultaneously inducing a sense of fullness. In a trial involving 338 obese adults, those administered with retatrutide witnessed unprecedented weight loss outcomes. Over 48 weeks, participants lost an average of 24% of their body weight, equivalent to more than four stone each. Notably, retatrutide demonstrated greater efficacy in women, with a weight loss of 28.5% compared to 21.2% in men. Retatrutide outshines other drugs, by activating three receptors and thus enhancing both weight loss and metabolic rate. Dr. Ania Jastreboff, director of the Yale Obesity Research Center, described the trial results as "striking," emphasizing the unprecedented degree of weight reduction achieved by retatrutide. In addition to its remarkable weight loss benefits, retatrutide also demonstrated positive effects on participants' health markers. Significant improvements were observed in blood pressure and blood sugar levels, with four in ten participants able to discontinue medication for high blood pressure. As retatrutide heralds a new era in obesity management, further research and trials are underway to explore its safety and long-term efficacy. Published in the New England Journal of Medicine, the study underscores the multifaceted benefits of retatrutide, offering hope for millions struggling with obesity worldwide. As retatrutide awaits approval for NHS use, its anticipated impact on obesity treatment could be nothing short of revolutionary.
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Comparing Mounjaro to Other Weight Loss Medications
When discussing weight loss medications, it’s essential to consider how Mounjaro stacks up against other options, such as Ozempic (semaglutide) and Wegovy (also semaglutide). Clinical data suggest that Mounjaro users can achieve higher average weight loss percentages compared to those on Ozempic or Wegovy.
Mounjaro's Success Rate for Weight Loss: Clinical Trial Results
Recent studies have provided encouraging insights into the effectiveness of Mounjaro for weight loss. One of the most notable studies, known as SURMOUNT-1, involved approximately 700 participants with obesity or overweight conditions. The participants were divided into groups receiving different dosages of tirzepatide over a 176-week period. Participants in the study experienced varying degrees of weight loss depending on the dosage. Over the course of the study, many participants maintained clinically meaningful weight loss.
What to Expect in the First Month on Mounjaro
If you’re contemplating taking Mounjaro, then you may be wondering what you can expect. According to Scott McDougall, a registered pharmacist and co-founder of The Independent Pharmacy, it takes around eight to 72 hours for the medication to reach peak levels in your system.
First Week
You may feel a reduction in your appetite during this time, and you could also begin experiencing common side effects, such as diarrhoea and headaches. Your body will become more used to Mounjaro in the future, but it’s expected that this first week could be a little rough. If you’re concerned about how you're feeling during this stage, it’s worth contacting your GP for more information.
Second Week
McDougall writes that your sweet, sugary cravings could be reduced dramatically after taking your second dose of Mounjaro. He states that you’ll probably be eating and drinking less than before, and that side effects may diminish due to your body becoming used to the substance you’re injecting into it. To stop becoming tired or hungry, it’s recommended you eat a healthy, balanced diet, and that you continue to consume plenty of liquids.
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Third Week
The third dose of Mounjaro is where users’ bodies begin to become accustomed to the drug, according to McDougall. “At this point most people notice their side effects becoming milder or disappearing completely, although some may find that their symptoms are more stubborn,” the pharmacist explains. “Though you may not notice any weight loss just yet, you could find that your appetite is consistently reduced and you’re eating less than normal.”
One Month On
According to clinical trials, people who make it to week four on Mounjaro are likely to lose up to 4 percent of their starting weight, with 6 percent being reported after two months, as per The Care Pharmacy. Your body is also likely to be adjusted to the weight-loss drug at this stage. If you haven’t reported any significant side effects to your GP, then your doctor may now increase your dose of the medication. By the four month mark, you may also be making healthier meals and increasing your level of exercise, building better habits for the future.
Common Side Effects of Mounjaro and Ozempic
Most of the early side effects Mounjaro can cause in the body are gastrointestinal in nature, writes Boots Online Doctor. These include nausea, vomiting, diarrhoea and constipation. And as your body adapts to the drug dosage, these side effects will reportedly settle.
Some common side effects associated with GLP-1 medications are:
- Nausea
- Vomiting
- Headache
- Dizziness
- Stomach pain
- Constipation
- Diarrhea
- Heartburn
- Indigestion
- GERD (gastroesophageal reflux disease)
- Bloating
- Allergic reaction
Ozempic® should be taken once a week, on the same day every week, at any time of the day. Ozempic® may be taken with or without food. After injecting Ozempic® exactly as instructed, some people may experience some bleeding at the injection site. Press on the area lightly with a gauze pad or cotton ball. You may inject under the skin of your stomach/abdomen, thigh, or upper arm. Be sure to change the injection site after each weekly injection, and do not use the same site for each injection.
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Other common side effects could include: fatigue, feeling lightheaded and gallstones. Users on Mounjaro have also previously reported suffering from gastroesophageal reflux, injection site reactions and hair loss.
Less Common but Serious Side Effects
Extended use of tirzepatide and semaglutide may cause additional side-effects that although uncommon, it’s important to be aware of them. These include digestive problems, gallbladder problems, pancreatitis, increased risk for parathyroid cancer, kidney issues, and hypoglycemia.
It’s important that you contact a medical professional if you experience a rash after injecting Mounjaro, or if your lips, tongue and/or throat begin to swell. Shortness of breath and dizziness, and/or fainting are also causes for concern.
If you experience any of these side effects and find that they are lasting an extended period of time or are worsening to a considerable degree, contact your medical team immediately.
The Importance of Lifestyle Changes
While Mounjaro presents a significant breakthrough in weight loss solutions, it is crucial to remember that medication alone cannot yield optimal results. Integrating lifestyle changes such as diet and exercise is vital for maximizing the benefits of this treatment. Combining Mounjaro with a balanced diet and regular physical activity can enhance weight loss outcomes. Developing healthy habits aids weight maintenance long after discontinuing the medication.
Is Ozempic Safe?
Ozempic was developed in 2012 and has been widely used for diabetes for the past 11 years. It’s important to stick to the FDA approved GLP-1 medications when choosing a weight loss product. Compounded salt alternative of these medications are available, but are not FDA approved and may not be as safe or effective as those that are FDA approved.
Considerations and Precautions
These drugs are not for everyone which is why it’s important to talk to your doctor before you start taking them. You cannot be on this medicine if you have Multiple Endocrine Neoplasia (MEN syndrome), pancreatitis, gastroparesis, severe constipation, or are going into surgery. Many people experience weight loss while taking the drug, and some report losing muscle mass which is why it’s important to be under doctor supervision while taking these drugs.
The Future of Weight Loss Medications
As tirzepatide and semaglutide medications are relatively new, many long-term effects are not yet known. Further research and trials are underway to explore its safety and long-term efficacy.