GLP-1 stands for Glucagon-Like Peptide-1. It is a hormone that your own intestine produces naturally when you eat. Its main function is to tell your pancreas to release insulin to control blood sugar, and to tell your brain that you have eaten enough.

GLP-1 medications are synthetic versions of that natural hormone. They are administered by subcutaneous injection (under the skin) and act by mimicking your natural GLP-1, but with a much longer duration. The main ones are:

• Semaglutide: Ozempic (diabetes), Wegovy (obesity), Rybelsus (tablet)
• Tirzepatide: Mounjaro (diabetes), Zepbound (obesity) - dual GLP-1/GIP agonist
• Liraglutide: Saxenda (obesity), Victoza (diabetes)
• Survodutide: in development, dual GCG/GLP-1 agonist

Yes and no. Both contain the same active ingredient, semaglutide. The difference lies in the indication and dosage:

• Ozempic: approved for type 2 diabetes. Maximum dose: 2 mg/week.
• Wegovy: approved for weight loss. Maximum dose: 2.4 mg/week.
• Wegovy HD: new high-dose formulation (7.2 mg/week) approved in March 2026 for patients requiring additional weight loss.

In the SURMOUNT-5 study, patients on Zepbound lost 47% more weight than those on Wegovy.

Mounjaro is the brand name for tirzepatide approved for the treatment of type 2 diabetes. Although not officially approved for weight loss in all countries, studies showed patients with diabetes lost between 5.5 kg and 11 kg on average.

Zepbound is the same active ingredient as Mounjaro (tirzepatide), but specifically approved for chronic weight management in people with obesity or overweight with comorbidities. In studies, patients lost an average of 21% of their body weight at the 15 mg dose.

These medications were originally developed to treat type 2 diabetes because they mimic GLP-1, a hormone that stimulates insulin release and reduces blood sugar.

During clinical trials, researchers noticed that patients lost significant weight. So manufacturers conducted specific studies for obesity, and in 2021 Wegovy (high-dose semaglutide) was approved for weight loss. Then Zepbound (tirzepatide) arrived in 2023.

It depends on the medication:

• Ozempic: not approved for weight loss. Using it solely for weight loss is off-label use. Not illegal (doctors can prescribe off-label), but it's not the approved indication.
• Wegovy and Zepbound: yes, they are specifically approved for weight loss.

The ethical problem: when people use Ozempic for weight loss, it creates shortages for diabetic patients who truly need it.

No. GLP-1 does not directly burn fat. It does not speed up metabolism or make your body burn calories faster. What it does is reduce appetite so you eat less. Fat loss occurs because you consume fewer calories, not because the medication "melts" fat.

GLP-1 crosses the blood-brain barrier and acts on GLP-1 receptors in the hypothalamus (the brain region that regulates appetite) and in the circumventricular organs. What it does:

• Increases satiety (you feel full earlier)
• Decreases hunger (you don't feel like eating)
• Reduces cravings (especially for high-calorie foods)
• Modulates the central amygdala, a brain region associated with desire, reducing dopamine release during hedonic eating (eating for pleasure)

Many patients describe exactly that: the "voice that craves food" disappears. That constant thinking about the next meal, that anxiety about snacking between meals… goes away. It's a very liberating experience for people with obesity or binge eating disorders.

Yes, it works even without conscious dieting, because the medication automatically reduces your appetite. You eat less because you're not hungry, not because you're making a willpower effort.

But studies show that combining it with diet and exercise enhances results. And most importantly, it helps you maintain weight when you stop treatment.

This is the big question without a definitive answer. Studies show that when treatment is stopped, most people regain lost weight (rebound effect). That's why many doctors consider obesity a chronic disease requiring chronic treatment, like hypertension or diabetes.

But there is no single answer. Some people manage to maintain weight after stopping the medication if they have permanently changed their habits.

According to approved indications in Europe and the US:

• BMI ≥30 (obesity) → ✅ Yes
• BMI 27-29.9 (overweight) with at least one comorbidity → ✅ Yes
• BMI <27 without comorbidities → ❌ No

Comorbidities include: type 2 diabetes, hypertension, dyslipidaemia, obstructive sleep apnoea, cardiovascular disease.

No. These medications are indicated for obesity or overweight with comorbidities, not for losing a few cosmetic kilos. The side effects (nausea, vomiting, diarrhoea) are not worth it for such small weight loss.

Wegovy (semaglutide) is approved for adolescents aged 12 years or older with obesity (BMI ≥ 95th percentile) and weight above 60 kg. In studies, adolescents lost an average of 16.1% of their BMI.

No. It is contraindicated in pregnancy. Animal studies have shown risks to the foetus. Also, weight loss during pregnancy is not recommended.

If you become pregnant while taking GLP-1, you should stop it immediately and consult your doctor. It hasn't been proven dangerous, but as a precaution it is not used in pregnancy.

Given that semaglutide has a half-life of approximately 1 week, it will be almost completely eliminated in 5 weeks. But many doctors recommend waiting 2-3 months as a precaution.

There are no safety studies in lactation. As a precaution, it is not recommended.

It is a subcutaneous injection (under the skin), not intravenous. It comes in a pre-filled pen similar to those used by diabetics for insulin.

Subcutaneous. The needle is very fine and short, only penetrating the layer of fat under the skin.

Recommended injection sites are:

• Abdomen (at least 5 cm around the navel)
• Thigh (front part)
• Arm (back part)

It is recommended to rotate the injection site each week to avoid irritation.

The needles are very fine (usually 32G). The prick hurts very little, similar to a small sting. Many patients barely notice it.

If you forget a dose:

• If less than 5 days have passed: you can take it as soon as you remember.
• If more than 5 days have passed: skip the missed dose and take the next one on your usual day.

Do not take a double dose to make up for it.

Before first use: store in refrigerator (2°C to 8°C).

After first use: can be stored at room temperature (max 30°C) for 28 days (Wegovy/Ozempic) or 21 days (Mounjaro).

Do not freeze or expose to extreme heat.

Weight loss is not linear. The first months less is lost (low doses), and from month 3-4 it accelerates:

• 1 month: 2-4 kg
• 3 months: 7-10 kg
• 6 months: 12-16 kg
• 12 months: 18-25 kg (~21% of body weight with tirzepatide)

In clinical studies:

• Wegovy (semaglutide 2.4 mg): mean loss of 15% of body weight
• Zepbound (tirzepatide 15 mg): mean loss of 21% of body weight. One third of patients lost more than 25% of their weight
• Wegovy HD (7.2 mg): new high dose approved in March 2026 for patients requiring additional weight loss

Many patients notice reduced appetite in the first week, even with the low initial dose (0.25 mg). Maximum effect is reached after several weeks of treatment.

Approximately 10-15% of patients do not respond significantly to treatment (lose less than 5% of body weight). Reasons are unclear, but may include genetic or metabolic factors.

Yes. In studies, patients who stopped treatment regained most of the lost weight in the following months. Hunger returns and without the medication, it's difficult to maintain caloric restriction.

Yes, nausea is the most common side effect, affecting up to 40-50% of patients at the start of treatment or when increasing the dose. It usually improves over time.

Yes. Acute pancreatitis is a rare but serious complication associated with GLP-1 agonists. Regulatory agencies have issued alerts highlighting the risk of severe pancreatitis, including rare cases of necrotising pancreatitis.

Warning signs: severe abdominal pain that may radiate to the back, persistent nausea and vomiting. If these occur, stop the medication and go to A&E.

In rodent studies, semaglutide and tirzepatide increased the incidence of thyroid C-cell tumours (a rare type of thyroid cancer). This has not been confirmed in humans, but as a safety precaution, they are contraindicated in people with personal or family history of medullary thyroid carcinoma (MTC) or with multiple endocrine neoplasia syndrome type 2 (MEN-2).

Yes. In studies, between 20% and 40% of lost weight can be muscle mass, not fat. This is a high percentage, similar to what occurs with very restrictive diets without exercise.

How to prevent it:

• Strength training (weights, squats, etc.)
• Adequate protein intake (1.2-1.5 g per kg of body weight)
• Gradual weight loss, not aggressive

Hair loss (telogen effluvium) is a side effect reported by some patients. It occurs due to the metabolic stress of rapid weight loss, not a direct effect of the medication on the hair follicle. It is usually temporary and reversible.

Cases of non-arteritic anterior ischaemic optic neuropathy (NAION), a condition that can cause vision loss, have been reported in patients taking semaglutide. It is very rare, but you should be alert to changes in vision.

"Ozempic face" is a non-medical term describing the hollowed, aged appearance some people develop after losing weight very quickly. By losing facial fat (especially in cheeks, temples and periorbital area), skin can become lax and wrinkles more pronounced.

This is not a direct effect of the medication, but of rapid weight loss. It also occurs with extreme diets or bariatric surgery.

Dermatologists recommend the protocol known as "sculpt and lift":

• Combination of poly-L-lactic acid (Sculptra) and midface hyaluronic acid filler
• Improves facial harmony and skin quality
• In a study of 41 patients, significant benefit was seen in cheeks, jawline and periorbital area

Important: Optimise nutrition before treatment, with 1 g of protein per pound of weight to support collagen synthesis.

Similar to the face, rapid fat loss also affects the buttocks, which can become flatter and more lax. This is an effect of weight loss, not the medication. It can be treated with fillers, fat transfer or specific gluteal exercises.

According to dermatologists, hyaluronic acid fillers may last less in patients taking GLP-1 due to the metabolic and nutritional changes associated with rapid weight loss. Hence they recommend "preparing the skin nutritionally" before aesthetic treatments.

Yes, there is promising research in this area:

• GLP-1 agonists appear to attenuate the "wanting" and pleasure associated with both food and substances of abuse
• Population analyses show that semaglutide exposure is associated with fewer hospitalisations related to alcohol use disorder and fewer diagnoses of this disorder
• A randomised clinical trial examining semaglutide vs placebo in patients with alcohol use disorder has been published

Although this is a very active area of research, it is not currently an approved use.

This is an interesting phenomenon. GLP-1 acts on the brain's reward centres. Some patients report losing interest in other pleasurable activities such as alcohol, gambling or compulsive shopping. Studies with small molecule oral medications show they modulate the reward circuit in the central amygdala, reducing hedonic feeding.

In the UK (private prescription prices):

• Wegovy (low dose: 0.25-1 mg): ~£160
• Wegovy (medium dose: 1.7 mg): ~£210
• Wegovy (high dose: 2.4 mg): ~£260
• Mounjaro (2.5-5 mg): ~£240
• Mounjaro (7.5-10 mg): ~£320
• Mounjaro (12.5-15 mg): ~£400
• Saxenda (full dose): ~£420
• Ozempic (black market): £450-650
• Wegovy HD (7.2 mg): ~£1100

In the UK, the NHS does not routinely fund Wegovy, Saxenda or Mounjaro for weight loss. Access is limited through specialist weight management services. Only GLP-1 medications for type 2 diabetes (Ozempic, Victoza, Trulicity) are funded under certain criteria.

The use of Ozempic for weight loss has caused a global shortage affecting diabetic patients who truly need it. Health authorities have had to prioritise its use for diabetics and alert about the problem.

A gut hormone (glucagon-like peptide-1) that regulates appetite and blood sugar. Medications mimic it.

Yes, both are semaglutide. Ozempic is approved for diabetes and Wegovy for obesity (higher doses).

Tirzepatide (Mounjaro/Zepbound) usually produces greater weight loss (up to 22%) because it acts on two hormones (GLP-1 + GIP).

Between 12-22% of body weight depending on the medication and the person.

Only under medical prescription. It is not for losing a few cosmetic kilos.

Rapid facial fat loss that can make you look more aged or hollow.

It is very common to regain a large portion if lifestyle changes are not maintained.

No. It is recommended to stop well in advance if planning a pregnancy.

No. Fake or poorly compounded versions are dangerous and are being pursued by the FDA.

It does not cause addiction. It may reduce "addiction" to food and, in some cases, to other rewards (alcohol, shopping).