Retatrutide Dosage:
What Current Research Shows

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

In clinical trials, retatrutide was usually started at a dose of 2mg once per week.

This starting dose wasn’t intended to produce the maximum weight loss straight away, but to help the body adjust and reduce the risk of side effects.

Further reading: Retatrutide side effects

In the Phase 2 obesity trial, a small number of participants started directly at 4mg once weekly, rather than starting at 2mg.

Starting at 4mg was found to be slightly harder to tolerate, with more digestive side effects early on, which is why later trials moved toward using 2mg as the standard starting dose.

Because of its good tolerability and effectiveness, 2mg once weekly is now the standard starting dose being used in ongoing Phase 3 clinical trials.

Retatrutide dosing in clinical trials follows a gradual increase schedule, known as titration. This allows the body to adjust to the medication while reducing the risk of side effects.

Doses are increased every four weeks.

As the dose increases, the average weight loss also increases. This dose-dependent effect is one of the key findings from retatrutide clinical trials.

However, you can still stay on a lower dose and lose weight. It is not mandatory to increase the dose

Clinical research hasn’t established a single official maintenance dose for retatrutide, since the drug is still investigational. However, the Phase 2 trial shows how maintenance doses were handled in practice.

In clinical trials, the amount of weight people lost on retatrutide depended on the maintenance dose they reached and how long they stayed on treatment.

After gradually increasing from the starting dose, participants remained on maintenance doses of 4mg, 8mg, or 12mg once weekly, and weight loss continued to increase 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

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

• 12mg: average weight loss of up to 28.7% of body weight
• 8mg: continued substantial weight loss, typically reaching around 22–25%
• 4mg: sustained weight loss of approximately 15–18%

This longer-term data shows that weight loss with retatrutide does not stop at one year, and can continue to improve over time, especially at higher maintenance doses.

Overall, clinical trials show that retatrutide produces better results with higher doses.

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.

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.