How weight loss pills work: a nutritionist's guide
Published: 28 July 2026
Read time: 3 min read
Following the launch of the daily Wegovy weight loss pill in the UK in July 2026, many people are questioning how it differs from weight loss injections and whether it is as effective.
To separate fact from fiction, PortionIQ nutritionist Mark Gilbert answers some of the most common questions about how weight loss pills work, their potential side effects and why good nutrition remains essential during treatment.
How do weight loss pills work?
The Wegovy weight loss pill contains semaglutide, the same active ingredient used in Wegovy injections. It mimics a naturally occurring hormone called GLP-1, helping to reduce appetite, slow digestion and increase feelings of fullness.
The main difference is how the medication is taken. Users must fast for at least eight hours, take the tablet with no more than 120ml of plain water and wait at least 30 minutes before eating, drinking or taking other medication.
This routine may appeal to people who would prefer not to use needles, while others may find a once-weekly injection easier. Because the tablet must be absorbed through the stomach, a higher dose is needed to achieve the intended effect.
Do weight loss pills work?
Clinical trials suggest that weight loss pills can be effective when combined with a reduced-calorie diet and regular physical activity.
Research shows participants taking a 25mg daily Wegovy pill lost an average of 13.6% of their starting body weight over 64 weeks, compared with 2.4% among those taking a placebo. Results will vary between individuals and medication should form part of a wider approach to weight management.
Are weight loss pills safe?
Licensed weight loss pills are considered safe for eligible patients when prescribed by a qualified healthcare professional and taken correctly. However, they are not suitable for everyone and should only be obtained through a regulated pharmacy or medical provider.
Unregulated weight loss pills and supplements sold online may contain unknown or unsafe ingredients. Always speak to a healthcare professional before beginning treatment.
It is also important to consider nutrition. A suppressed appetite can make it harder to consume enough protein, fibre, vitamins and minerals, increasing the risk of nutritional deficiencies and muscle loss.
What are the side effects of weight loss pills?
As the Wegovy pill and injection contain the same active ingredient, they can cause similar side effects. Common side effects include:
-
Nausea and vomiting
-
Acid reflux or heartburn
-
Diarrhoea or constipation
-
Headaches and fatigue
Eating less can also make it harder to meet the body’s nutritional needs. If protein intake is too low, people may lose a greater proportion of lean muscle alongside body fat. A reduced food intake may also contribute to vitamin and mineral deficiencies.
Read more about the common challenges experienced by people taking GLP-1 medication.
Do weight loss pills cause irregular bowel movements?
Some weight loss pills can change how often you go to the toilet. Semaglutide may cause diarrhoea in some people and constipation in others, particularly when beginning treatment or increasing the dose.
Gradually increasing your fibre intake and drinking enough fluid may help support healthy digestion. Speak to your healthcare provider if symptoms are severe, persistent or accompanied by significant pain.
What can I eat on a weight loss pill?
GLP-1 medications work by significantly reducing appetite, which means many people consume substantially fewer calories. While this supports weight loss, it also increases the risk of nutritional shortfalls if food choices are not carefully considered. When people are eating much smaller portions, every meal needs to deliver maximum nutritional value.
Ensuring enough high-quality protein is particularly important to help preserve lean muscle mass, support strength and maintain metabolic health, while fibre-rich foods can support digestion, gut health and help manage side effects such as constipation. A reduced appetite can also make it harder to meet micronutrient needs, which is why prioritising nutrient-dense foods is crucial throughout treatment.
For inspiration, explore our nutritionist-approved meal and snack schedule for people taking GLP-1 medication.
Supporting your nutrition while losing weight
Good nutrition is fundamental to healthy weight loss. Addressing potential gaps in protein, fibre, vitamins and minerals can help protect muscle mass, support energy levels and promote better long-term health.
For nutritional support during weight loss, discover PortionIQ’s range of portion-controlled bites, drinks, shakes and soups. Each product contains at least 21 vitamins and minerals, alongside protein and fibre to help support people eating smaller portions.
Support your nutrition with PortionIQ
Weight loss pills can help reduce your appetite, but eating less should not mean missing out on essential nutrients. Explore PortionIQ’s high-protein, high-fibre range and give your body the nutritional support it needs throughout your weight loss journey.