1. At-a-glance comparison
| Mounjaro | Wegovy | Ozempic | |
|---|---|---|---|
| Active drug | Tirzepatide | Semaglutide 2.4mg | Semaglutide 1.0mg |
| Mechanism | Dual GIP / GLP-1 | GLP-1 only | GLP-1 only |
| Japan approval | Type 2 diabetes | Obesity (Mar 2023) | Type 2 diabetes |
| Avg weight loss | ~20% (15mg) | ~15% (2.4mg) | ~6-9% (1mg) |
| Frequency | Once weekly | Once weekly | Once weekly |
| Pen type | Single-use Ateos | Multi-dose FlexTouch | Multi-dose FlexTouch |
| Private price / mo (Japan) | ¥6,000-24,000 (2.5mg) | ¥30,000-60,000 | ¥15,000-30,000 |
2. What each drug actually is
All three are GLP-1 receptor agonists — a class of injectable medications originally developed for type 2 diabetes that turned out to be highly effective for weight loss. They work by mimicking gut hormones that signal satiety to the brain, slowing stomach emptying, and improving how the body handles glucose.
Mounjaro (tirzepatide)
Made by Eli Lilly. Mounjaro is the only drug in this comparison that acts on two receptors at once: both GIP and GLP-1. This dual mechanism is the main reason Mounjaro consistently outperforms GLP-1-only drugs in weight-loss trials. Doses available in Japan: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, and 15mg, escalated gradually over months.
Wegovy (semaglutide 2.4mg)
Made by Novo Nordisk. Wegovy is the higher-dose obesity-specific formulation of semaglutide. Doses escalate from 0.25mg through 0.5mg, 1.0mg, 1.7mg, up to a maintenance dose of 2.4mg. It is the same active molecule as Ozempic, just at higher maximum strength.
Ozempic (semaglutide up to 1.0mg)
Also Novo Nordisk. Ozempic is the diabetes-strength version of semaglutide, with maximum dose of 1mg per week (or 2mg in some markets). It is approved for type 2 diabetes globally, and is widely used off-label for weight loss because the active ingredient is identical to Wegovy at lower strength.
3. Approval status in Japan
This is where things get interesting for international patients:
| Drug | Japan-approved indication | Available for weight loss? |
|---|---|---|
| Mounjaro | Type 2 diabetes (Apr 2023) | Yes, via private (self-paid) care |
| Wegovy | Obesity (Mar 2023, launched Feb 2024) | Yes, the only on-label option |
| Ozempic | Type 2 diabetes | Yes, via private (self-paid) care |
For international patients without Japanese national health insurance, the practical effect is the same across all three drugs: each is accessible only as private (self-paid) medical care. The approval-status distinction matters more for residents who can use NHI coverage for Wegovy under strict criteria — for tourists, all three are private care pricing regardless.
Counterintuitively, Wegovy’s on-label status means it cannot be discounted below the official price list, while Mounjaro and Ozempic prescribed off-label for weight loss have more pricing flexibility. The result: Japanese clinics often offer Mounjaro at lower private prices than Wegovy.
4. Effectiveness: how much weight do you lose?
Clinical trial data — particularly the head-to-head SURMOUNT-5 study published in 2024 — gives us the clearest comparison:
| Drug | Trial | Duration | Avg body weight loss |
|---|---|---|---|
| Mounjaro 15mg | SURMOUNT-5 | 72 weeks | ~20.2% |
| Wegovy 2.4mg | SURMOUNT-5 | 72 weeks | ~13.7% |
| Mounjaro 5mg | SURMOUNT-1 | 72 weeks | ~15.0% |
| Wegovy 2.4mg | STEP-1 | 68 weeks | ~14.9% |
| Ozempic 1mg | SUSTAIN-1 | 30 weeks | ~4.5% |
The headline finding: Mounjaro at maximum dose produces roughly 1.5x more weight loss than Wegovy in direct comparison. Ozempic, used off-label for weight loss, produces noticeably less because the maximum dose is half of Wegovy’s.
Every clinical trial cited above included structured nutrition counseling and physical activity guidance alongside the medication. The percentages are not what you get from medication alone — they reflect the combination. Be skeptical of any clinic that markets these drugs as standalone solutions.
5. Cost in Japan as a private patient
Japanese private-clinic pricing varies based on the clinic’s structure, the included services, and whether consultation is bundled. Typical monthly ranges for international patients:
| Drug + dose | Monthly cost | USD equivalent |
|---|---|---|
| Mounjaro 2.5mg (starting) | ¥6,000-24,000 | $40-160 |
| Mounjaro 5mg (standard) | ¥15,000-42,000 | $100-280 |
| Wegovy (private clinic) | ¥30,000-60,000 | $200-400 |
| Ozempic 0.5-1mg | ¥15,000-30,000 | $100-200 |
Compared to the same medications in the US, Japan is dramatically cheaper across the board:
- Ozempic: $169 in Japan vs $936 in the US (per KFF analysis)
- Wegovy: ~$290 in Japan vs $1,349 in the US
- Mounjaro: ~$160 in Japan vs $1,000+ in the US
For multi-month plans, Japanese clinics commonly offer 10-20% discounts on 3 and 6-month bundles, since a single prescription can cover up to 6 months under personal-use rules.
6. Side effects compared
All three drugs share the same general side-effect profile because they work on overlapping pathways. The differences are subtle:
Mounjaro Dual-action
Wegovy GLP-1 only
Ozempic GLP-1, lower dose
Two patterns to note: (1) Wegovy at maximum dose tends to cause more gastrointestinal side effects than Mounjaro because semaglutide is harder on the GI tract at the higher 2.4mg dose; (2) Ozempic is the most tolerable but also produces less weight loss because of the lower dose ceiling.
Serious-but-rare side effects (pancreatitis, gallstones, thyroid C-cell tumor warning) are roughly equivalent across the three drugs, since they all share GLP-1 mechanism.
7. Which one is right for you?
There’s no universal answer, but here are practical decision frames:
Choose Mounjaro if:
- You want the most weight loss per yen — best effectiveness-to-cost ratio in Japan
- You have significant weight to lose (more than 15kg)
- You can tolerate self-injection with a single-use pen each week
Choose Wegovy if:
- You want the regulatory comfort of an on-label obesity drug
- You qualify for Japanese national health insurance coverage (most international patients do not)
- You’ve already tried Ozempic and tolerated semaglutide well
Choose Ozempic if:
- You want a gentler entry point with lower side-effect risk
- You only need modest weight loss (5-10kg)
- You also have type 2 diabetes — Ozempic on-label fits this case directly
Whichever drug you choose, treatment should be guided by a licensed physician who reviews your medical history, monitors your response, and adjusts the plan over time. Clinics that ship medication after only a one-page questionnaire are skipping the medical evaluation step — and the risk falls on you. Reputable providers in Japan include video consultation, regular follow-up, and nutrition guidance.
8. Frequently asked questions
Is Mounjaro or Wegovy more effective?
In the head-to-head SURMOUNT-5 trial published in 2024, Mounjaro 15mg produced ~20% body weight loss at 72 weeks, versus ~14% for Wegovy 2.4mg. Mounjaro’s dual GIP/GLP-1 mechanism appears to give it the effectiveness edge. Individual results vary based on dose, adherence, and lifestyle factors.
Can I get Wegovy in Japan as a tourist?
Yes. Wegovy has been approved in Japan for obesity treatment since March 2023. Tourists can be prescribed it through private (self-paid) medical care since Japanese national health insurance is not available to non-residents. Expect ¥30,000-60,000 per month at private clinics.
Is Ozempic the same as Wegovy?
Both contain semaglutide, but at different doses with different approved indications. Ozempic maxes out at 1mg per week (approved for diabetes); Wegovy goes up to 2.4mg (approved for obesity). Wegovy generally produces more weight loss because of the higher dose ceiling.
Which weight loss drug is cheapest in Japan?
Mounjaro starting dose (2.5mg) is typically the cheapest entry point at ¥6,000-24,000 per month. Ozempic ranges ¥15,000-30,000. Wegovy is usually the most expensive at ¥30,000-60,000 per month for private care.
Can I switch between these drugs mid-treatment?
Yes, switching is medically straightforward but requires physician supervision. Most commonly, patients move from semaglutide (Ozempic or Wegovy) to tirzepatide (Mounjaro) for stronger effect, or from Mounjaro to semaglutide if they tolerate it better. There’s no washout period required, but dose levels are not 1:1 equivalent, so your doctor will adjust starting dose accordingly.
Do all three need refrigeration?
Yes. Unopened pens for all three drugs must be stored at 2-8°C (refrigerator). Once a pen is in use, Mounjaro Ateos can stay at room temperature up to 21 days; Wegovy and Ozempic FlexTouch pens can stay at room temperature up to 28 days. For travel, always carry in an insulated cooler with gel packs in hand luggage.
Sources & further reading
- SURMOUNT-5 (Mounjaro vs Wegovy head-to-head) — New England Journal of Medicine, 2024
- SURMOUNT-1 — tirzepatide for obesity, NEJM 2022
- STEP-1 — semaglutide 2.4mg for obesity, NEJM 2021
- Eli Lilly — Mounjaro prescribing information (Japan)
- Novo Nordisk — Wegovy and Ozempic prescribing information (Japan)
- KFF Health System Tracker — International price comparison of weight loss drugs
- PMDA, Japan — Drug approval database