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Why aren’t GLP-1 doses determined by your weight?
Weight loss injections aren’t weight-dependent, unlike many medications. This can seem strange; wouldn’t it make sense to get a higher dose if you weigh more?
The simple reason is that weight loss injections target receptors in your brain and gut, and their effects aren’t proportional to your body weight. So taking a higher dose doesn’t necessarily mean it will be more effective; instead, it might just increase your risk of side effects, which could be dangerous.
Medically reviewed by
Craig Marsh, Independent Prescriber
Why are other medication doses determined by your weight?
Many medications are weight-dependent, meaning their dosage is based on how much you weigh. For example, antibiotics are commonly dosed according to body weight because everyone has a different total weight. The more you weigh, the more medication you’ll need to achieve the same concentrations throughout your body compared to someone lighter. Taking too low a dose wouldn’t effectively treat infections, while a higher dose could lead to serious side effects. So it’s important to find the right dose.
Giving the correct dose is especially important for children and older people, as their bodies can be more sensitive to medications. This is why common medications like paracetamol and ibuprofen are age and weight-dependent for children. In adults, there’s a recommended dose for use over 24 hours, but in children, the dosage must be adjusted according to their weight.
Weight-dependent medications aren’t the only ones measured this way. Other medications are calculated based on different factors, such as diabetes treatments, which are often administered based on your blood sugar levels. Typically, you take a dose based on how high or low your blood sugar is – taking the wrong amount could lead to hyperglycemia (high blood sugar) or hypoglycemia (low blood sugar), both of which pose health risks.
While you might expect weight-loss injections to work similarly, they work differently.
Why aren’t weight loss injection doses determined by your weight?
Weight loss injections target your receptors. For example, Wegovy targets your GLP receptors, while Mounjaro targets both your GLP and GIP receptors. These receptors help regulate appetite and feelings of fullness.
The number of receptors you have isn’t proportional to your total body weight, so just because you weigh more doesn’t mean you have more of these receptors. This is why weight loss injections aren’t weight-dependent, and everyone starts on the same dose and gradually works their way to the maintenance dose.
While increasing your dose can be more effective, it also increases the risk of side effects. The chosen dose is based on years of research and clinical trial data. It’s selected to be well-tolerated, safe, and effective.
Why do people increase their GLP-1 dose if it isn’t dictated by your body weight?
When using weight-loss injections, you need to follow a specific dosing schedule. Depending on the medication, your dose will usually increase every four weeks until you reach a maintenance dose.
The reason your dose gradually increases is primarily to help your body adjust to the medication and reduce the risk of side effects, particularly nausea, vomiting and diarrhoea. Gradually increasing the dose also allows you to eventually reach a level that provides effective weight loss.
When you start taking Wegovy, you may feel full more quickly and notice a decrease in your appetite, which can make you less inclined to eat. Additionally, you might experience gastrointestinal side effects like vomiting and nausea, particularly noticeable at the beginning of treatment. But as your body adjusts to the medication over time, these effects may become less intense, and the side effects become more manageable. As a result, your dose is increased so you can continue to experience weight-loss benefits from the medicine.
So why doesn’t your dose keep increasing indefinitely? Research has shown that the maintenance dose is sufficient to continue seeing effective weight loss. Taking a higher dose also increases the risk of side effects, so there’s a careful balance between effectiveness and safety.
Finding the right GLP-1 dose for you
There are many types of weight loss injections, and finding the right one for you can be a highly individualised process based on biology, medical history, treatment eligibility and how well you tolerate the medication, rather than starting weight.
Our clinicians are here to help and can guide you to the most suitable medication for your needs. Simply answer a few questions online to find the options that are best for you.
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