Mounjaro vs Wegovy vs Ozempic: How They Differ

Mounjaro, Wegovy, and Ozempic are injectable GLP-1 medications (weight-management pens) that differ in their active ingredients and indications. Mounjaro is tirzepatide, while Ozempic and Wegovy are semaglutide. All are controlled drugs that require a prescription and use under a doctor’s supervision. Results vary by individual, and you should not seek them out and use them on your own.

What are GLP-1 medications and how do they work?

GLP-1 medications (glucagon-like peptide-1 receptor agonists) act by mimicking a hormone in the body involved in regulating hunger and blood sugar. The main general mechanism is to help you feel full faster and stay full longer, slow the emptying of food from the stomach, and help regulate blood sugar. They are therefore used both in the treatment of type 2 diabetes and, for certain indications, in weight management.

What is important to understand from the outset is that these are not “diet drugs” to be used as one pleases. They are medications with specific indications that require an individual assessment of suitability. Moreover, the results obtained usually depend on lifestyle changes — both diet and exercise together — not injections alone.

Within this group, Mounjaro differs slightly in that it acts through two mechanisms, both GIP and GLP-1, whereas Ozempic, Wegovy, and Saxenda act primarily through GLP-1.

How do Mounjaro, Wegovy, Ozempic, and Saxenda differ?

The main differences lie in the “active ingredient,” “mechanism,” “injection frequency,” and “registered indication.” In summary:

• Mounjaro = tirzepatide, acting through two mechanisms (GIP + GLP-1), injected once weekly. Its original registered indication focuses on type 2 diabetes (under the brand name Zepbound, it is registered for weight management in some countries).
• Wegovy = semaglutide, acting on GLP-1, injected once weekly, registered for weight management in people who meet the appropriate criteria.
• Ozempic = semaglutide (the same active ingredient as Wegovy but a different brand name and dose), injected once weekly, registered primarily for the treatment of type 2 diabetes.
• Saxenda = liraglutide, acting on GLP-1, injected once daily, registered for weight management.

The registered indication of each product may differ from country to country and may be updated periodically. The choice of which to use must therefore always be based on current information and a doctor’s assessment.

Who is each one suitable for?

The short answer is “it depends on a doctor’s individual assessment.” None is suitable for everyone, because the choice depends on many factors, such as underlying conditions (especially type 2 diabetes), body mass index, other health conditions, current medications, the injection frequency the user finds convenient, and the registered indication.

Broadly speaking, for people who also have type 2 diabetes, a doctor may consider a medication indicated for diabetes, while for people whose goal is weight management according to medical criteria, a doctor may consider a medication registered for weight management. Injection frequency is another factor — some people find a once-weekly injection more convenient than a daily one.

The important thing is that you should not choose a medication yourself based on reviews or word of mouth, because each person’s circumstances are different. A doctor’s assessment helps reduce risk and helps tailor a treatment plan to each individual’s health.

Common side effects and precautions

GLP-1 medications can have side effects. The most common are usually related to the digestive system, such as nausea, vomiting, diarrhea or constipation, abdominal pain, and loss of appetite. These symptoms often occur at the start or during dose adjustment, and their severity varies by individual.

There are also precautions and conditions that are uncommon but should be watched for, such as pancreatitis, gallbladder problems, and — in people who are also taking other diabetes medications — a possible risk of low blood sugar. For this reason, monitoring by a doctor is important. If you notice anything abnormal, such as severe, persistent abdominal pain, you should stop and consult a doctor immediately.

These precautions are an important reason why this group of medications must be used under a doctor’s supervision, rather than bought and injected on your own.

Who should not use them

There are groups who should not use these medications or who require more caution than usual, which a doctor will assess, such as:

• Women who are pregnant, planning to become pregnant, or breastfeeding
• People with a history of allergy to drugs in this group
• People with a personal or family history of medullary thyroid cancer or MEN 2 syndrome (per the warnings of certain products)
• People with a history of pancreatitis or certain gastrointestinal diseases
• Children and adolescents, for whom the indications and permitted ages differ across products

The list above is a partial set of examples, not a complete list. An actual assessment requires a health history and examination by a doctor, so you should tell your doctor about all underlying conditions and medications you are taking before starting.

Can weight come back after stopping the medication?

There is a tendency for some of it to return. In clinical studies (such as the extension of the STEP 1 trial), it was found that after stopping the medication, a number of participants regained some weight over time, reflecting the fact that obesity is a chronic condition that often requires ongoing care.

This means that using this group of medications is not a one-time fix, but part of a long-term care plan that includes changes to eating habits and exercise. Long-term results vary by individual and depend on planning together with a doctor. Stopping the medication should likewise be done under a doctor’s guidance — you should not stop on your own abruptly.

Authenticity and safety: why it must be used under a doctor

In Thailand, injectable GLP-1 medications are classified as controlled drugs that require a prescription and use under a doctor’s supervision; they are not products that can be bought and sold freely. The reason is that these medications have specific indications, contraindications, and side effects, and require appropriate dose adjustment and monitoring.

A major risk to watch for is “grey-market” products or items of unknown origin, which may be counterfeit, improperly stored, dosed inconsistently with the label, or contaminated — all of which greatly increase health risks. Obtaining medication from a proper medical facility, after an assessment by a doctor, is therefore an approach that helps reduce the risks of counterfeits and inappropriate use.

For safety and authenticity, you should choose a medical facility with doctors in charge. You can find more information about the doctors who provide care at Onnyx Clinic.

How to get started at Onnyx

At Onnyx Clinic, considering the use of a weight-management pen begins with a consultation and assessment by a doctor, to review your health history, underlying conditions, current medications, and goals. The doctor will then explain the options, risks, and possible side effects before a decision is made together, and will plan periodic monitoring. See an overview of the service at weight-management pens under a doctor’s supervision.

As for price, the cost of each approach falls within a wide range and varies greatly, depending on the type of medication, the dose, and the care plan the doctor assesses on an individual basis, so a fixed price cannot be stated. Ask about details and price ranges via LINE.

Please remember that GLP-1 medications are controlled drugs with both benefits and risks. You should always consult a doctor before starting, and you should not seek them out and use them on your own.

Always consult a doctor before starting — ask for information and book an assessment with a doctor via LINE: @onnyxclinic

References

• SURMOUNT-1: Tirzepatide Once Weekly for the Treatment of Obesity (NEJM)
• Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension (PubMed)
• FDA: News & Events — GLP-1 and weight-management drug approvals
• Novo Nordisk receives FDA approval for Saxenda (liraglutide) for chronic weight management
• Thai Food and Drug Administration (FDA)