Retatrutide Dosage Guide

Important: this is for educational purposes only, as retatrutide is still investigational and not approved for real-world use.

In clinical trials, retatrutide was typically started at a dose of 2mg once weekly.

This starting dose was not designed to produce maximum weight loss immediately. Instead, it allows the body time to adjust to the medication, helping to reduce the risk of common side effects, particularly digestive symptoms such as nausea, bloating, and diarrhoea.

Further reading: Retatrutide side effects

In the Phase 2 obesity trial, a small number of participants started directly on 4mg once weekly, rather than beginning at 2mg. However, this higher starting dose was more difficult to tolerate, with participants experiencing a higher rate of digestive side effects early in treatment.

As a result, later studies shifted toward a more gradual approach, using 2mg once weekly as the standard starting dose, with dose increases over time if needed.

Due to its strong balance of tolerability and effectiveness, 2mg once weekly is now the standard starting dose used in ongoing Phase 3 clinical trials.

Retatrutide dosing in clinical trials follows a gradual increase schedule, known as dose titration. This approach allows the body time to adjust to the medication, helping to reduce the risk of side effects and improve overall tolerability.

In most studies, the dose was increased every four weeks, with participants slowly progressing to higher doses over time.

Clinical trial results also showed a clear dose-dependent effect, meaning that higher doses generally led to greater average weight loss. This is one of the key findings from retatrutide research.

However, it’s important to note that meaningful weight loss can still occur at lower doses. Increasing the dose is not mandatory, and some individuals may achieve good results while remaining on a lower, better-tolerated dose.

Clinical research has not yet established a single official maintenance dose for retatrutide, as the medication is still investigational. However, Phase 2 trial data provides a clear picture of how maintenance dosing was used in practice.

In clinical trials, the amount of weight loss depended largely on the maintenance dose reached and how long participants remained on treatment. After gradually increasing from the starting dose, participants stayed on maintenance doses of 4mg, 8mg, or 12mg once weekly, with weight loss continuing to improve over time.

By 48 weeks, significant average weight loss was seen at all maintenance doses:

• 4mg: average weight loss of 17.1% of body weight
• 8mg: average weight loss of 22.8% of body weight
• 12mg: average weight loss of 24.2% of body weight

With longer treatment lasting up to 68 weeks, weight loss continued, particularly at higher doses:

• 4mg: continued weight loss, approximately 18% of body weight
• 8mg: continued weight loss, approximately 25% of body weight

• 12mg: average weight loss of up to 28.7% of body weight

This longer-term data shows that weight loss with retatrutide can continue beyond one year, rather than plateauing early, especially at higher maintenance doses.

Overall, clinical trials consistently demonstrate a dose-dependent effect, with higher maintenance doses producing greater average weight loss.

Because retatrutide is still being studied, expectations, access, and long-term use are still evolving as more research is completed.

Administration

In clinical trials to date, retatrutide has been given as a once-weekly subcutaneous injection (an injection just under the skin).

Dosing is introduced slowly and the gradual build-up is an important part of how the drug is tested, rather than jumping straight to higher doses.

Availability

Retatrutide is still in Phase 3 clinical trials and has not yet been approved by the UK’s Medicines and Healthcare products Regulatory Agency (MHRA).

These large-scale trials are expected to complete in 2026, which is the key step before any company can submit a marketing authorisation application.

This means the earliest realistic availability in the UK is likely to be in late 2026 or 2027.

Further reading: How to get retatrutide in the UK

Clinical trials show that retatrutide dosing follows a gradual increase from a low starting dose to a long-term maintenance dose, allowing the body to adjust while maximising weight loss.

Higher maintenance doses have consistently produced greater results, with average weight loss reaching up to 28.7% at the highest dose studied.