How GLP-1 weight-loss medicines work, and who they suit
Medically Reviewed by Dr. Pedro Yelamo Vera, MD
Licensed Physician No. 484814280 · Official Medical College of Bizkaia (Spain)Last reviewed: 12 October 2026
Weight loss medication explained by a GP in Spain: how GLP-1 medicines affect appetite and blood sugar, who they are for, and who should not use them.
You don't have to figure this out alone
Dr. Pedro Yelamo Vera is an independent, bilingual GP licensed in Spain. Book a 15-minute video consultation in English or Spanish for €50, with a private electronic prescription issued under Spanish law when clinically appropriate.
Weight loss medication has changed a lot in recent years. The best known are the GLP-1 medicines, given as a weekly or daily injection, and one is also made as a tablet. This guide explains how they work, what they are licensed for in Spain, and who should not use them. It is for expats, residents and travellers in Spain.
- GLP-1 medicines copy a gut hormone. They make you feel full sooner and help the body control blood sugar.
- Some are licensed for type 2 diabetes. Others are licensed for weight management in adults who meet set body mass index (BMI) rules.
- They are not used in pregnancy. People with some past health problems need extra care or should not use them.
- They work best as part of a wider plan that covers food, activity, sleep and support.
- A doctor decides if they are right for you after a full review.
What GLP-1 medicines are
GLP-1 stands for glucagon-like peptide-1. It is a hormone your gut releases after you eat. It tells the brain you have eaten. It also helps the pancreas release insulin when blood sugar rises.
GLP-1 medicines act like this hormone, but they last much longer in the body. Doctors call them GLP-1 receptor agonists. One newer medicine acts on two gut hormones at once: GLP-1 and GIP. It is called a dual GIP/GLP-1 agonist.
In the EU, these medicines are approved by the European Medicines Agency (EMA). That approval covers Spain. In Spain, all of them need a prescription from a doctor.
How they act on appetite and blood sugar
Appetite and fullness
GLP-1 medicines act on parts of the brain that control hunger. Many people feel less hungry and feel full on smaller meals. Some notice fewer cravings.
They also slow down the emptying of the stomach. Food stays in the stomach for longer. This adds to the sense of fullness. It also explains some side effects, such as nausea, and why your anaesthetist needs to know you take one.
Blood sugar
When blood sugar is high, these medicines help the pancreas release more insulin. They also lower glucagon, a hormone that raises blood sugar. Because this effect depends on blood sugar being high, the risk of low blood sugar is small on its own. The risk goes up when they are used with insulin or a sulfonylurea (an older type of diabetes tablet).
What this means in real life
Eating less is the main reason people lose weight on these medicines. They do not burn fat on their own. In large trials, average weight loss was larger with the medicine than with a placebo. In those trials, both groups also had advice on diet and activity. Results vary a lot from person to person, and some people lose little weight.
Which medicines are licensed in Spain, and for what
The table below gives the main active ingredients. Each has its own product information, called the ficha técnica in Spain. It sets out who the medicine is for. We do not list doses here. Only a doctor can decide on a dose for you.
| Active ingredient (brand) | Type | Licensed use in adults |
|---|---|---|
| Liraglutide (Saxenda) | GLP-1, daily injection | Weight management |
| Semaglutide (Wegovy) | GLP-1, weekly injection or daily tablet | Weight management |
| Semaglutide (Ozempic, Rybelsus) | GLP-1, weekly injection or daily tablet | Type 2 diabetes |
| Tirzepatide (Mounjaro) | Dual GIP/GLP-1, weekly injection | Type 2 diabetes and weight management |
The rules for weight management
For weight management in adults, the licence uses BMI. BMI is your weight in kilograms divided by your height in metres squared. The medicines are licensed for adults with:
- a BMI of 30 or more (obesity), or
- a BMI of 27 to under 30 (overweight) plus at least one health problem linked to weight.
Those health problems include prediabetes or type 2 diabetes, high blood pressure, high blood fats, obstructive sleep apnoea and heart disease. The exact list differs a little between products. In every case, the medicine is meant to go with a lower-calorie diet and more physical activity.
BMI is only a starting point. Waist size, where fat is stored and your overall health also matter. Our guide on obesity, BMI and waist size explains why.
Under-18s
Some of these medicines are also licensed for teenagers with obesity. A few are licensed for children with type 2 diabetes. Care for anyone under 18 should be led by a children's specialist team.
Public funding in Spain
Funding rules are not the same as the licence. Spain's public health system (SNS) funds semaglutide for some adults with type 2 diabetes. The rule in the Ministry of Health's price committee papers is for people with a BMI of 30 or more, used with other diabetes medicines, and it needs extra approval (visado). The committee has turned down public funding for the medicines licensed for weight management. We found no change to this in its 2026 papers up to September. Funding can change, so check with your pharmacist.
Who should not use them, or needs extra care
This is a general list. It does not replace a review of your own health.
- Pregnancy. These medicines are not used in pregnancy. The product information advises stopping some weeks before a planned pregnancy, and using contraception during treatment.
- Breastfeeding. They are generally not used while breastfeeding. Product rules differ, so this needs a talk with your doctor.
- Allergy. Anyone who has had an allergic reaction to the medicine or its contents must not use it.
- Past pancreatitis. The product information asks for caution. If pancreatitis is confirmed during treatment, the medicine must not be restarted.
- Some thyroid cancers. In animal studies, these medicines caused thyroid C-cell tumours. US labels say not to use them if you or a close relative had medullary thyroid cancer, or if you have MEN2 (multiple endocrine neoplasia type 2). EU product information does not list this as a formal ban, but doctors take it seriously.
- Other conditions. Use is not advised, or needs care, in type 1 diabetes, severe kidney or liver disease, severe heart failure, severe gastroparesis (a very slow stomach) and some eye problems from diabetes.
- Past eating disorders. A history of anorexia, bulimia or binge eating needs a careful, honest talk with your doctor first.
Some medicines also interact. The UK medicines regulator advises extra care with the contraceptive pill and tirzepatide. Our guide on weight-loss injection side effects covers this.
Why they go with changes to eating, activity and sleep
These medicines are licensed as an add-on, not a stand-alone fix.
- Food quality matters more when you eat less. You still need enough protein, fibre, fluids, vitamins and minerals.
- Activity helps keep muscle. Strength work helps protect muscle as weight falls.
- Sleep affects hunger. Short or broken sleep can raise appetite and cravings.
- Weight often returns after stopping. Habits built during treatment help when it ends. See our guide on stopping treatment and weight regain.
The World Health Organization (WHO) now has a guideline on these medicines for obesity. It treats them as a long-term option for adults who are not pregnant. It also says people may be offered support with eating and activity alongside them.
No one should cut food to extreme levels to speed things up. If you notice signs of disordered eating, tell your doctor.
What the Weight Optimization consultation looks at first
Dr. Pedro Yelamo Vera offers a 30-minute Weight Optimization consultation by video for people in Spain. It is a medical review of your weight and metabolic health. Medicine is only one possible part of the plan.
Before any medicine is discussed, the review covers:
- your weight history, BMI and waist size;
- health problems linked to weight, such as blood pressure, blood sugar, cholesterol or fatty liver;
- your current medicines, past treatments and allergies;
- pregnancy plans, contraception and breastfeeding;
- past pancreatitis, gallbladder, thyroid or kidney problems;
- any history of eating disorders, and your mood and sleep;
- recent blood tests, or which ones may be useful.
Our guide on blood tests before weight-loss treatment explains which tests are often checked. A video visit cannot replace a hands-on check. If one is needed, you will be told.
Where medicine is a reasonable option, it is a shared decision. Where clinically appropriate, following a genuine evaluation. Treatment and prescriptions are issued solely at the doctor's discretion based on evidence-based clinical guidelines. Any prescription is a private electronic prescription under Spanish law. Booking a visit does not mean a prescription will be issued.
Dr. Pedro Yelamo Vera is a GP licensed in Spain (Colegiado No. 484814280).
For a medical emergency, call 112 or go to the nearest local emergency department. Do not wait for a video consultation or an online reply.
Talk through your options with a GP
A 30-minute video review of your weight and health, in English or Spanish, while you are in Spain.
Use a pharmacy, not a website
Spain's medicines agency (AEMPS) has warned about fake GLP-1 products sold online and on social media. In Spain, prescription medicines cannot be sold online. Fill a prescription only at a pharmacy. Read more in our guide to fake weight-loss pens in Spain.
FAQ
How do GLP-1 medicines help with weight loss?
They copy a gut hormone that signals fullness. Most people feel less hungry and eat less. They also slow down the emptying of the stomach.
Who can be prescribed weight loss medication in Spain?
The licence is for adults with a BMI of 30 or more, or 27 or more with a weight-linked health problem. A doctor must also check that it is safe for you.
Are GLP-1 medicines funded by Spain's public health system for weight loss?
Public funding covers semaglutide only for some adults with type 2 diabetes, under set rules. Medicines licensed for weight management have not been approved for public funding. Rules can change, so ask your pharmacist.
Can I use these medicines if I am pregnant or breastfeeding?
They are not used in pregnancy and are generally not used while breastfeeding. If you plan a pregnancy, talk to your doctor well before you try to conceive.
Do I still need to change my diet and activity?
Yes. The medicines are licensed as an add-on to eating changes and more activity. These habits also help protect muscle and support you if treatment stops.
Will a Weight Optimization consultation always lead to a prescription?
No. Where clinically appropriate, following a genuine evaluation. Treatment and prescriptions are issued solely at the doctor's discretion based on evidence-based clinical guidelines.
Sources
- European Medicines Agency: Wegovy (semaglutide) overview and product information
- European Medicines Agency: Mounjaro (tirzepatide) overview and product information
- European Medicines Agency: Saxenda (liraglutide) overview and product information
- World Health Organization: global guideline on GLP-1 medicines for obesity (December 2025)
- Ministerio de Sanidad: agreements of the Interministerial Commission on Medicine Prices (CIPM)
- AEMPS: EMA and HMA warn of illegal medicines sold as GLP-1 analogues (2025)
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med 2021 (STEP 1)
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med 2022 (SURMOUNT-1)
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Medical Citations & Sources
This content is written and reviewed by a licensed physician with reference to the following official health authorities.
