Retatrutide Dosage for Weight Loss UK
If you've been reading about retatrutide — the so-called "triple G" weight loss drug — you've probably seen dosage charts floating around online. Some of them look convincingly medical. Most of them shouldn't be trusted. Retatrutide hasn't been approved yet, which means there is no officially licensed dose. What we do have is detailed clinical trial data, and that tells us quite a lot about how this medication is likely to be prescribed once it reaches the UK.
Here's what the evidence actually says.
At a glance
- Retatrutide is a once-weekly injection that targets three hormone receptors (GIP, GLP-1, and glucagon) — more than any approved weight loss medication
- In clinical trials, the starting dose was 2 mg per week, titrating up every four weeks to a maximum of 12 mg
- Phase 3 results show participants on the highest dose lost an average of 28.7% of their body weight — roughly 71 lbs (32 kg) — over 68 weeks
- Weight loss continued beyond 48 weeks at all dose levels, with the 8 mg dose reaching ~25% and the 4 mg dose reaching ~18% at 68 weeks
- The medication is still in Phase 3 clinical trials and has not been approved by the MHRA, FDA, or any other regulator
- UK availability is realistically expected in late 2027 or 2028 at the earliest
What is retatrutide and why does the dose matter?
Retatrutide is made by Eli Lilly — the same company behind Mounjaro (tirzepatide). Where Mounjaro activates two hormone receptors (GIP and GLP-1), retatrutide goes further by also activating the glucagon receptor. That third target is significant. Glucagon plays a direct role in energy expenditure and fat metabolism, which researchers believe explains why retatrutide has produced some of the highest weight loss figures seen in any clinical trial to date.
But more potent medications require more careful dosing. The three-receptor mechanism means the body needs time to adjust, and getting the dose right — particularly during the early weeks — has a meaningful impact on both tolerability and long-term results.
Retatrutide dosage schedule from clinical trials
Because retatrutide isn't approved yet, there's no official prescribing dose. What we have is the dosing protocol used across Eli Lilly's Phase 2 and Phase 3 clinical trials (the TRIUMPH programme). These trials give us a reliable picture of how the medication will likely be prescribed.
The standard titration schedule
In the Phase 3 TRIUMPH trials, participants followed a gradual dose escalation — increasing the dose every four weeks to allow the body to adjust and minimise gastrointestinal side effects.
| Week | Dose | Notes |
|---|---|---|
| 1–4 | 2 mg once weekly | Starting dose — primarily for tolerability, minimal weight loss expected |
| 5–8 | 4 mg once weekly | First therapeutic increase |
| 9–12 | 8 mg once weekly | Significant appetite reduction typically begins |
| 13 onwards | 12 mg once weekly | Maximum dose studied — associated with the greatest weight loss |
This four-step escalation over 12 weeks is the protocol most likely to inform how retatrutide is eventually prescribed.
All dosing schedules tested in clinical trials
The table above shows the primary Phase 3 route, but Lilly tested several different escalation paths across Phase 2 and Phase 3. Here's every schedule that's been studied:
| Target dose | Starting dose | Escalation schedule | Time to target dose |
|---|---|---|---|
| 0.5 mg* | 0.5 mg | No escalation | Immediate |
| 1 mg* | 1 mg | No escalation | Immediate |
| 4 mg* | 4 mg | No escalation | Immediate |
| 4 mg | 2 mg | 2 mg → 4 mg | 4 weeks |
| 8 mg | 2 mg | 2 mg → 4 mg → 8 mg | 8 weeks |
| 8 mg | 4 mg | 4 mg → 8 mg | 4 weeks |
| 9 mg | 2 mg | 2 mg → 4 mg → 6 mg → 9 mg | 12 weeks |
| 12 mg | 2 mg | 2 mg → 4 mg → 8 mg → 12 mg | 12 weeks |
| 12 mg | 2 mg | 2 mg → 4 mg → 6 mg → 9 mg → 12 mg | 16 weeks |
Fixed doses with no escalation — these were Phase 2 only and produced modest weight loss with fewer side effects, but were less effective than the escalated doses.
The 2 mg → 4 mg → 8 mg → 12 mg route over 12 weeks is the one Lilly settled on for the Phase 3 programme. But the range of schedules tested is worth knowing about — it suggests the final approved product may offer some flexibility in how quickly patients escalate, depending on tolerability.
Why the starting dose is 2 mg
In the Phase 2 trial published in the New England Journal of Medicine, several starting doses were tested: 1 mg, 2 mg, and 4 mg. The 2 mg starting dose hit the right balance. Participants tolerated it well, experienced fewer gastrointestinal side effects during the first month, and went on to achieve comparable long-term weight loss to those who started higher.
Don't expect dramatic changes in the first four weeks on 2 mg. That's not what it's there for. This phase is about letting your gut, your appetite signals, and your metabolism begin to adapt to a medication that acts on three different hormonal pathways simultaneously.
Clinical note: Most patients in the trials found that gastrointestinal side effects peaked during dose increases and settled within 1–2 weeks at each new level. The titration schedule is specifically designed around this pattern — each four-week block gives the body enough time to adjust before the next step up.
What about lower maintenance doses?
Not everyone in the trials went to 12 mg. Lilly is also studying 4 mg and 9 mg as maintenance doses in separate Phase 3 arms, recognising that some patients may achieve good results — or prefer to stay — at a lower level. The Phase 2 data supports this: participants on 8 mg lost an average of 22.8% of their body weight at 48 weeks, which is still substantially more than any currently approved medication.
This is an important nuance. The 12 mg dose grabbed headlines, but clinical practice is likely to be more individualised. Your prescriber would assess your response, side effects, and goals before deciding whether to push to the maximum dose or hold at a level that's working well for you.
How much weight can you lose on each dose?
The Phase 2 trial (published in the New England Journal of Medicine in June 2023) gave us the first detailed look at weight loss across different retatrutide doses at 48 weeks:
| Maintenance dose | Average weight loss at 48 weeks | What that looks like for someone weighing 100 kg |
|---|---|---|
| 1 mg | 8.7% | ~8.7 kg (19 lbs) |
| 4 mg | 17.1% | ~17.1 kg (38 lbs) |
| 8 mg | 22.8% | ~22.8 kg (50 lbs) |
| 12 mg | 24.2% | ~24.2 kg (53 lbs) |
| Placebo | 2.1% | ~2.1 kg (5 lbs) |
The Phase 3 TRIUMPH-4 trial, which reported results in December 2025, extended the treatment period to 68 weeks and found even greater results. Crucially, weight loss didn't plateau at 48 weeks — it continued across all dose levels:
| Maintenance dose | Average weight loss at 48 weeks | Average weight loss at 68 weeks |
|---|---|---|
| 4 mg | 17.1% | ~18% |
| 8 mg | 22.8% | ~25% |
| 12 mg | 24.2% | 28.7% |
That 28.7% figure at 12 mg translates to roughly 71 lbs (32 kg) of weight loss. To put that in context, the best results from Wegovy trials showed around 15% weight loss, and Mounjaro around 22%.
These are averages. Individual results varied considerably — some participants lost more, some less. But the consistency is remarkable: in the 12 mg group, 100% of participants lost at least 5% of their body weight, 93% lost at least 10%, and 83% lost at least 15%.
Retatrutide side effects at different doses
Side effects followed a clear dose-dependent pattern. Higher doses meant more gastrointestinal symptoms, particularly during the escalation phase.
| Side effect | 9 mg group | 12 mg group |
|---|---|---|
| Nausea | 38.1% | 43.2% |
| Diarrhoea | 34.7% | 33.1% |
| Constipation | 21.8% | 25.0% |
| Vomiting | 20.4% | 20.9% |
| Decreased appetite | 19.0% | 18.2% |
These figures come from the Phase 3 TRIUMPH-4 trial. A few things are worth noting here.
First, these are the rates for the entire treatment period. Most gastrointestinal symptoms occurred during dose escalation and improved once participants reached their maintenance dose. The trial protocols allowed flexibility — participants could stay at their current dose for an extra 2–4 weeks if side effects were particularly bothersome, and this didn't reduce their long-term weight loss.
Second, these rates are broadly comparable to what we see with Mounjaro and Wegovy. The addition of the glucagon receptor hasn't introduced a fundamentally different safety profile — it's the same class of side effects, at roughly similar rates.
Third, serious adverse events were rare. The overall safety profile was described as consistent with existing GLP-1 and GIP-based therapies. No new safety signals emerged.
Skin sensation changes
One side effect worth flagging separately: around 7% of trial participants reported changes in skin sensation — tingling, numbness, or increased sensitivity. These weren't severe and didn't cause anyone to stop treatment, but they're distinct from the gastrointestinal effects seen with other weight loss injections. It's not entirely clear whether this is related to the glucagon receptor activity or to rapid weight loss itself, and researchers are monitoring it in the Phase 3 programme.
Important: If you see retatrutide for sale online — as a "research peptide," a pre-mixed pen, or in any other form — it is not a legitimate pharmaceutical product. The MHRA has explicitly warned that such products are potentially dangerous, and in 2025 seized a major illicit weight loss medicine production facility. Retatrutide is only available within authorised clinical trials. You can report suspected counterfeit products via the MHRA Yellow Card Scheme.
How retatrutide dosage compares to Mounjaro and Wegovy
If you're already familiar with Mounjaro or Wegovy, here's how the dosing stacks up:
| Retatrutide | Mounjaro (tirzepatide) | Wegovy (semaglutide) | |
|---|---|---|---|
| Receptors targeted | GIP + GLP-1 + glucagon | GIP + GLP-1 | GLP-1 only |
| Starting dose | 2 mg weekly | 2.5 mg weekly | 0.25 mg weekly |
| Maximum dose | 12 mg weekly | 15 mg weekly | 7.2 mg weekly |
| Titration period | ~12 weeks | ~20 weeks | ~16 weeks |
| Best average weight loss | 28.7% at 68 weeks | 22.5% at 72 weeks | 21% at 72 weeks (7.2 mg) |
| Injection frequency | Once weekly | Once weekly | Once weekly |
| UK availability | Not yet approved | Available now | Available now |
The shorter titration period for retatrutide (12 weeks versus 16–20 for competitors) means patients reach the full therapeutic dose more quickly. Combined with the higher ceiling for weight loss, this could make retatrutide a particularly compelling option for people with a significant amount of weight to lose — or for those who haven't achieved their goals with existing treatments.
What happens after you reach your goal weight?
This is something the clinical trials haven't fully answered yet. The Phase 2 and Phase 3 studies were designed to measure weight loss during active treatment — they didn't specifically test what happens once you hit your target.
With currently approved medications like Wegovy and Mounjaro, the evidence is clear: most people need to continue treatment at some dose to maintain their results. Some stay on their full dose. Others step down to a lower maintenance level. The weight tends to return if the medication is stopped entirely — this is consistent across every GLP-1 medication studied to date.
Retatrutide will likely follow the same pattern. Lilly hasn't published specific maintenance or discontinuation data yet, but it's reasonable to expect that ongoing treatment — potentially at a reduced dose — will be needed to sustain results. Your prescriber would work with you to find the right balance between maintaining weight loss and minimising long-term medication use.
How much will retatrutide cost in the UK?
Nobody knows the exact price yet, but we can make an educated guess based on how Lilly prices Mounjaro.
Mounjaro currently costs between £150 and £370 per month in the UK depending on the dose and provider, with the lowest doses being cheapest and the 15 mg dose at the top end. Since retatrutide is made by the same company, uses a similar once-weekly pen format, and targets a similar patient population, pricing is likely to fall in a comparable range — though the triple-receptor mechanism and stronger efficacy data could justify a premium.
For context, Wegovy currently costs between £120 and £300 per month depending on the dose and provider. The pattern across the market is consistent: monthly costs for weight loss injections sit somewhere between £120 and £400 for most patients.
We'll update this section once Lilly announces UK pricing. If you're exploring treatment options now, you can check current Mounjaro and Wegovy pricing on our site.
When will retatrutide be available in the UK?
This is the question we get asked most. The honest answer: not soon, but the timeline is becoming clearer.
Retatrutide is currently in Phase 3 clinical trials across multiple indications — obesity, type 2 diabetes, knee osteoarthritis, obstructive sleep apnoea, chronic low back pain, and liver disease. The first Phase 3 trial (TRIUMPH-4) reported successful results in December 2025, with seven further readouts expected throughout 2026.
Eli Lilly is expected to file for FDA approval in late 2026 or early 2027. MHRA approval in the UK typically follows 4–12 months after the FDA — though it's worth noting the MHRA has recently shown a willingness to move quickly on obesity treatments. In January 2026, the MHRA approved the higher 7.2 mg dose of Wegovy before the FDA did, making the UK the first country in the world to authorise that strength.
The realistic timeline for UK availability is late 2027 to mid-2028. NHS access through NICE would likely follow 6–18 months after that. When retatrutide is approved, it will almost certainly be available from private online prescribers — like heySlim — before it reaches the NHS.
We know that's frustrating if you're looking for options now. In the meantime, treatments like Mounjaro and Wegovy are available and clinically proven — and for many people, they deliver life-changing results while we wait for the next generation of medications to arrive.
The bottom line
Retatrutide's dosing protocol — starting at 2 mg weekly and titrating up to 12 mg over 12 weeks — has produced the most impressive weight loss results of any medication studied to date. The Phase 3 data showing 28.7% average body weight loss is remarkable, and the side effect profile is broadly similar to existing treatments.
But it isn't available yet. And the dosage charts and "calculators" you'll find online aren't prescribing guides — they're marketing for unregulated products that carry real risks. The safest approach is to wait for regulatory approval and work with a qualified prescriber when the time comes.
If you're considering weight loss treatment now, a medical consultation can help you understand which of the currently available options — including Mounjaro and Wegovy — might be right for you.
Frequently asked questions
What is the starting dose of retatrutide?
In Phase 3 clinical trials, the starting dose is 2 mg once weekly, administered as a subcutaneous injection. This dose is primarily for tolerability — significant weight loss typically begins once the dose increases to 4 mg or 8 mg. Some earlier Phase 2 trials used a 1 mg or 4 mg starting dose, but 2 mg has become the standard across the TRIUMPH programme.
How often do you take retatrutide?
Retatrutide is a once-weekly subcutaneous injection — the same frequency as Mounjaro and Wegovy. It's injected into the abdomen, thigh, or upper arm, and the injection site should be rotated each week.
What is the maximum dose of retatrutide?
The highest dose studied in clinical trials is 12 mg once weekly. At this dose, participants in the Phase 3 TRIUMPH-4 trial lost an average of 28.7% of their body weight over 68 weeks. Lower maintenance doses of 4 mg and 9 mg are also being studied in other Phase 3 trials.
How does retatrutide dosage compare to Mounjaro?
Both medications use a weekly injection and a gradual dose escalation. Mounjaro starts at 2.5 mg and can increase to 15 mg, with titration taking around 20 weeks. Retatrutide starts at 2 mg and reaches its maximum of 12 mg in approximately 12 weeks — a shorter escalation period. The key difference is that retatrutide acts on three hormone receptors compared to Mounjaro's two.
Can you buy retatrutide in the UK?
No. Retatrutide is not approved for sale in the UK and is only available within authorised clinical trials. Products sold online claiming to contain retatrutide are unregulated and potentially dangerous — both the MHRA and FDA have issued warnings about these products. You can report suspected counterfeit medicines to the MHRA Yellow Card Scheme. UK availability is expected in late 2027 or 2028, following regulatory approval.
Why isn't there a retatrutide dosage calculator?
Because retatrutide isn't approved, there are no standardised dosing guidelines to base a calculator on. The schedules used in clinical trials may differ from the final approved protocol. Any "dosage calculator" you find online is not a legitimate medical tool — it's likely marketing for unregulated peptide products. Once retatrutide is licensed, your prescriber will determine your dose based on your individual response, medical history, and tolerability. It won't be a one-size-fits-all formula.
Do you need to stay on retatrutide after reaching your goal weight?
We don't have definitive data on this yet. With currently approved medications like Wegovy and Mounjaro, most patients need to continue treatment to maintain their weight loss. The evidence consistently shows that weight tends to return when GLP-1-based medications are stopped. Retatrutide will likely follow the same pattern, though Lilly hasn't published specific maintenance or discontinuation data. Your prescriber will work with you to find the right long-term approach.
This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting any treatment.