Mounjaro vs. Ozempic: Which one wins? A practicing internist gives an honest comparison
“Which is better, Mounjaro or Ozempic?”
I have been asked this very often in my clinic over the past six months.
I will give you the answer first: comparing which one “wins” is, honestly, nonsense.
However, I can answer the question of “which one is right for you.”
Today, I will talk about that. I will talk honestly about everything: the differences in how the two drugs work, a comparison of clinical data, the cost, and the differences in side effects. My goal is to provide the information needed for those who are thinking, “I don’t know which one to choose.”
【What you will learn in this article】
🎯 What is Ozempic? A quick review first
🔬 Differences in mechanism: GLP-1 vs. GIP+GLP-1
⚡ Comparison of weight loss effects: Comparing honestly with clinical data
🔍 Three quick facts (side effects, cost, and insurance differences)
🏥 Which one is recommended for whom
✅ Summary
🎯 What is Ozempic? A quick review first
The generic name for Ozempic is semaglutide. It is a GLP-1 receptor agonist manufactured by the Danish company Novo Nordisk.
In Japan, it was approved in 2021 as a treatment for type 2 diabetes, and it has since appeared for obesity under the name “Wegovy” (the ingredient is the same semaglutide, but the dosage is different).
Ozempic is also a once-weekly subcutaneous injection. The fact that it acts only on the GLP-1 receptor is the biggest difference from Mounjaro.
Let’s briefly review what GLP-1 does to the body.
Promotes insulin secretion (lowers blood sugar levels)
Slows down stomach movement (suppresses post-meal blood sugar spikes)
Acts on the appetite center in the brain (suppresses appetite)
Suppresses glucagon secretion (reduces glucose release from the liver)
This effect alone is impressive enough, but Mounjaro also adds the effects of GIP to this.
🔬 Differences in mechanism—GLP-1 vs. GIP+GLP-1
The biggest difference between Mounjaro and Ozempic is "whether or not it acts on GIP".
What is GIP?
GIP (glucose-dependent insulinotropic polypeptide) is a hormone secreted by K cells in the small intestine when you eat.
What is interesting is that GIP not only sends a command to the pancreas to "release insulin," but also has the aspect of acting directly on fat cells to change fat metabolism.
Furthermore, research has revealed that GIP and GLP-1 create a synergistic effect when they work together. It's like 1+1 equals 3 instead of 2.
"But wasn't it said in the past that GIP has the opposite effect on obesity?"
That is a sharp observation. In fact, previous studies suggested that "GIP works in a direction that stores fat." However, recent research has produced many results showing that "activating GIP receptors makes it easier to lose weight due to the synergistic effect with GLP-1." It could be said that the development of Mounjaro took advantage of that contradiction.
This is an area where research is still ongoing, and I think we will learn more details in the future.
⚡ Comparison of weight loss effects—Comparing honestly with clinical data
Now, let's look at the data to see which one actually makes you lose more weight.
Mounjaro (tirzepatide) SURMOUNT-1 trial
| Dosage | Weight loss rate (72 weeks) |
|------|-----------------|
| 5mg/week | -15.0% |
| 10mg/week | -19.5% |
| 15mg/week | -20.9% |
Ozempic (semaglutide) STEP-1 trial
| Dosage | Weight loss rate (68 weeks) |
|------|-----------------|
| 2.4mg/week | -14.9% |
Although it is difficult to compare them on the same playing field (because the trial designs are different), looking simply at the numbers:
Mounjaro maximum dose (15mg): approx. 21%
Semaglutide maximum dose (2.4mg): approx. 15%
The current assessment is that Mounjaro has a greater weight loss effect.
I have several patients who have used both medications, and the general impression is that many feel, 'The way my appetite drops is completely different since switching to Mounjaro.'
However, there are significant individual differences.
These figures are just averages. Some people lose over 20% with Ozempic, while others lose less than 10% with Mounjaro. How the body reacts varies greatly from person to person.
🔍 Trivia ①: Comparison of side effects
Common side effects for both include nausea, diarrhea, constipation, and loss of appetite. This could be called the fate of GLP-1 receptor agonists.
Regarding notable differences, data suggests that nausea is slightly less common with Mounjaro (possibly due to the effect of GIP). However, individual differences are significant, and some people find Mounjaro to be more difficult.
Injection site reactions (redness and itching) can occur with both, but they almost always subside within a few days.
🔍 Trivia ②: Comparison of costs (as of 2024, for out-of-pocket expenses)
These are the estimated costs when receiving a prescription out-of-pocket for the purpose of 'wanting to cure obesity' where insurance cannot be used.
| Medication | Estimated monthly cost (out-of-pocket) |
|---|------------------------|
| Mounjaro | Approx. 20,000–40,000 yen (depending on dosage and clinic) |
| Ozempic | Approx. 20,000–30,000 yen (depending on dosage and clinic) |
Neither is cheap. Furthermore, you need to continue as long as you are seeing results (if you stop, you will regain the weight). It is important to consider whether you can continue long-term, including the financial burden.
Also, online clinics are increasing rapidly, and while some claim to be 'very cheap,' I recommend checking whether regular follow-ups (blood tests, weight/blood pressure management, etc.) are being conducted appropriately.
🔍 Trivia ③: A doctor's real-life experience
In my outpatient clinic, there was a case where a patient who had been using Ozempic for many years switched to Mounjaro. The reason for the switch was, 'I lost 6kg with Ozempic, but the weight stopped moving after that.'
Three months after switching to Mounjaro, they lost another 8kg. The patient themselves said, 'The urge to eat is different.'
However, another patient experienced severe nausea as soon as they switched to Mounjaro and went back to Ozempic. The way the medication works really varies greatly by individual, and honestly, I cannot say for sure which one is absolutely better.
🏥 This one is recommended for these types of people
As a rough guide, I will share what I feel are the 'suitability' factors in my outpatient practice.
People who might be suited for Mounjaro
Those whose progress has plateaued with GLP-1 drugs like Ozempic
Those who want to lose more weight (target weight loss rate over 15%)
Those who have difficulty controlling type 2 diabetes (also has a strong blood glucose-lowering effect)
People who might be better suited for Ozempic
Those who have never used GLP-1 drugs and are trying them for the first time (start with a drug that has a proven track record)
Those who want to keep costs as low as possible
Those who prioritize evidence of cardiovascular protection (Ozempic has extensive data from trials like SUSTAIN-6)
People for whom neither is suitable
Those with a history or family history of medullary thyroid carcinoma
Those with a history of pancreatitis
Those who are pregnant or planning to become pregnant
Ultimately, consultation with your attending physician is essential. Please do not decide based solely on information from social media or note.
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Summary
✅ Mounjaro is a dual GIP+GLP-1 agonist, while Ozempic is a GLP-1 receptor agonist
✅ Statistically, Mounjaro shows greater weight loss efficacy (approx. 21% vs. approx. 15% at maximum dosage)
✅ Mounjaro may have slightly fewer side effects like nausea (varies greatly by individual)
✅ Costs for both are 20,000 to 40,000 yen per month (if self-pay), with no significant difference
✅ Ozempic has extensive evidence for cardiovascular protection
✅ Rather than asking "which is better," it is correct to choose based on your own constitution, goals, and situation
✅ With both, "if you stop, you regain weight." It is important to continue while improving lifestyle habits
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