Getting retatrutide dosage right is the difference between manageable side effects and treatment-ending nausea.

The data is clear: participants who started at higher doses or escalated too quickly had nearly double the gastrointestinal side effects compared to those who titrated gradually.

This guide provides complete dosage charts based on clinical trial protocols, reconstitution calculations, injection instructions, and practical guidance for every phase of treatment.

Important disclaimer: Retatrutide is an investigational drug not yet approved by the FDA. These protocols are based on clinical trial data and are provided for educational purposes. Always work with a qualified healthcare provider.

Quick reference: retatrutide dosage chart

This chart reflects the escalation schedule used in Phase 2 and Phase 3 clinical trials:

Standard titration protocol (2mg start → 12mg target)

Alternative protocols by target dose

Target: 8 mg maintenance

Target: 4 mg maintenance

Key principle: Start low, go slow. Increase every 4 weeks unless side effects require holding at current dose longer.

For context on why dosing matters for this peptide, see our GLP-3 peptide guide which explains retatrutide's mechanism.

Understanding retatrutide dosing

Why gradual titration matters

Retatrutide activates three powerful receptor systems simultaneously. Your body needs time to adjust to each:

1. GLP-1 receptor: Slows gastric emptying, reduces appetite

2. GIP receptor: Enhances insulin signaling, affects fat metabolism

3. Glucagon receptor: Increases energy expenditure, promotes fat oxidation

Jumping to high doses overwhelms these systems, causing:

• Severe nausea and vomiting

• Treatment discontinuation

• Longer overall time to reach therapeutic doses

The data: In the Phase 2 NEJM study, participants who started at 4 mg instead of 2 mg had significantly higher rates of gastrointestinal side effects. Slow titration doesn't just feel better—it actually leads to better adherence and outcomes.

Dosing fundamentals

Administration:

• Once weekly subcutaneous injection

• Same day each week (consistency matters)

• Preferably at the same time of day

Half-life: Approximately 6 days, supporting weekly dosing

Dose escalation: Every 4 weeks, unless:

• Side effects require holding current dose

• Individual tolerance suggests faster/slower progression

• Healthcare provider recommends adjustment

Clinical trial doses tested

The Phase 2 obesity trial tested multiple dosing arms:

Key insight: 8 mg produces nearly the same results as 12 mg with fewer side effects—making it a potential "sweet spot" for many users.

Detailed week-by-week protocol

This expanded chart includes practical guidance for each phase:

Phase 1: Initiation (Weeks 1-4)

Dose: 2 mg once weekly

What to expect:

• Reduced appetite (often noticed within days)

• Possible mild nausea (usually transient)

• Some reduction in food cravings

• Minimal weight loss during this phase

Tips:

• Establish your injection routine

• Track symptoms in a journal

• Note your baseline weight and measurements

• Don't expect dramatic results yet

Side effects at this phase:

• Usually mild if present

• Most common: slight nausea, mild fullness

• If severe: contact your provider before escalating

Phase 2: First escalation (Weeks 5-8)

Dose: 4 mg once weekly

What to expect:

• More noticeable appetite suppression

• Possible increase in nausea (typically resolves in 1-2 weeks)

• Beginning of measurable weight loss

• Some may notice improved energy

Tips:

• Eat smaller, more frequent meals

• Avoid high-fat and fried foods

• Stay well-hydrated (minimum 64 oz water daily)

• If nausea is severe, hold at 2 mg for 2 more weeks

Side effects at this phase:

• GI symptoms often peak here

• Nausea, occasional vomiting, bloating possible

• Most symptoms improve by week 7-8

Phase 3: Building dose (Weeks 9-12)

Dose: 6 mg once weekly

What to expect:

• Significant appetite reduction

• Noticeable weight loss (often 5-10% by week 12)

• Body adapting to medication

• Side effects often improving from week 5-8

Tips:

• Continue hydration focus

• Prioritize protein intake to preserve muscle

• Consider light exercise if energy permits

• Monitor for any new symptoms

Note: Some protocols skip 6 mg and go directly from 4 mg to 8 mg. Discuss with your provider.

Phase 4: Therapeutic dose (Weeks 13-16)

Dose: 8 mg or 9 mg once weekly

What to expect:

• Strong appetite suppression

• Significant ongoing weight loss

• Possible temporary GI flare during escalation

• Many reach 10-15% weight loss by this phase

Tips:

• This is where most people stabilize

• 8 mg may be sufficient for many—higher isn't always better

• Continue lifestyle optimization

• Regular check-ins with healthcare provider

Phase 5: Maximum dose (Week 17+)

Dose: 12 mg once weekly (if tolerated and needed)

What to expect:

• Maximum therapeutic effect

• Continued weight loss (averaging 20%+ by 48 weeks in trials)

• GI side effects may be manageable or may persist

• Some achieve 25-30%+ weight loss

Tips:

• Not everyone needs to reach 12 mg

• Lower doses may provide sufficient results

• Balance efficacy with tolerability

• Maintenance may involve dose reduction

For general peptide dosing principles, see our peptide dosage calculator guide.

Reconstitution and calculation guide

If using lyophilized (powder) retatrutide, you'll need to reconstitute before injection.

Reconstitution basics

You'll need:

• Retatrutide vial (typically 5 mg, 10 mg, or 20 mg)

• Bacteriostatic water

• Sterile syringe for reconstitution

• Insulin syringes for injection

• Alcohol swabs

Standard reconstitution volumes:

Dose calculation formula

Formula:

Dose (mg) ÷ Concentration (mg/mL) = Volume to inject (mL)

Example calculations (10 mg vial with 2 mL water = 5 mg/mL):

Important: If your calculated volume exceeds 1 mL, consider:

• Using a higher concentration (less water)

• Splitting into two injection sites

• Using a larger vial size

Vial requirements by dose

How many vials do you need?

For detailed reconstitution instructions, see our how to reconstitute peptides guide.

Injection technique

Proper injection technique ensures consistent dosing and minimizes discomfort.

Step-by-step injection guide

Preparation:

1. Wash hands thoroughly with soap and water

2. Gather supplies: reconstituted retatrutide, insulin syringe, alcohol swabs

3. Check solution is clear (discard if cloudy or contains particles)

4. Allow solution to reach room temperature if refrigerated

Drawing the dose:

1. Clean vial top with alcohol swab, let dry

2. Draw calculated volume of air into syringe

3. Insert needle into vial, inject air

4. Invert vial and withdraw exact dose

5. Remove air bubbles by tapping syringe gently

6. Confirm correct volume

Injection:

1. Choose injection site (abdomen, thigh, or upper arm)

2. Clean site with alcohol swab, let dry completely

3. Pinch skin to create fold (optional but recommended)

4. Insert needle at 90° angle (or 45° if very lean)

5. Depress plunger slowly and steadily

6. Wait 5-10 seconds before withdrawing needle

7. Apply gentle pressure with gauze if needed

8. Dispose of needle in sharps container

Injection site rotation

Rotate weekly to prevent:

• Lipohypertrophy (fatty lumps)

• Injection site reactions

• Inconsistent absorption

Rotation pattern example:

Spacing: Each injection should be at least 1 inch from previous sites.

For storage guidance, see our peptide storage guide.

Side effect management by dose

Understanding what to expect at each dose level helps you prepare and respond appropriately.

Side effects by dose level

Note: These are approximate rates from clinical trials. Individual experiences vary.

Managing common side effects

Nausea:

• Eat smaller, more frequent meals

• Avoid fatty, fried, and spicy foods

• Stay upright after eating (don't lie down)

• Ginger tea or ginger supplements may help

• Take anti-nausea medication if prescribed

Diarrhea:

• Stay well-hydrated

• Consider electrolyte replacement

• Avoid trigger foods

• Take OTC anti-diarrheal if persistent

Constipation:

• Increase fiber intake gradually

• Drink plenty of water

• Consider stool softeners

• Light exercise can help

Appetite loss (beyond desired effect):

• Prioritize protein-rich, nutrient-dense foods

• Eat even when not hungry (small amounts)

• Consider protein shakes if solid food is difficult

When to contact your provider

Contact immediately if:

• Severe abdominal pain

• Signs of pancreatitis (severe pain radiating to back)

• Severe vomiting that won't stop

• Signs of dehydration

• Allergic reaction (rash, swelling, difficulty breathing)

• Unusual symptoms not listed here

Contact for guidance if:

• Side effects persist beyond 2 weeks

• Side effects interfere with daily life

• You're considering dose adjustment

• You've missed doses and need guidance

For comprehensive safety information, see our peptide safety guide.

Dosing adjustments and special considerations

Holding or reducing dose

When to hold at current dose:

• Moderate-to-severe GI symptoms

• Symptoms that haven't resolved after 3-4 weeks

• Any concerning side effects

When to reduce dose:

• Symptoms intolerable at current level

• Significant weight loss plateau doesn't require maximum dose

• Maintenance phase after reaching goals

How to hold:

• Stay at current dose for an additional 2-4 weeks

• Then attempt escalation again

• If symptoms recur, may need to maintain at lower dose

Missed dose protocol

If you miss a dose:

• Take it as soon as you remember if within 4-5 days

• If more than 5 days, skip and resume normal schedule

• Never double dose to make up for missed injection

If you frequently miss doses:

• Set weekly reminders

• Choose a consistent day (many choose Sunday)

• Consider adjusting day if schedule conflicts

Population considerations

For those with kidney impairment:

• Limited data available

• Slower titration may be warranted

• More frequent monitoring recommended

• Discuss with provider before starting

For those with liver impairment:

• Retatrutide is hepatically metabolized

• Caution in moderate-to-severe liver disease

• May need dose adjustments

• Requires provider guidance

For women:

• Similar dosing to men in trials

• May have stronger appetite suppression effects

• Some may need slower titration

• Contraception recommended during treatment

For older adults:

• May need slower titration

• Increased monitoring for dehydration

• Start at lowest dose

• More frequent check-ins

Comparing retatrutide dosing to other medications

Retatrutide vs. semaglutide (Wegovy)

Retatrutide vs. tirzepatide (Zepbound)

Key differences:

• Retatrutide adds glucagon receptor activity

• Slightly greater weight loss potential

• Similar side effect profiles

• Similar titration approach

For comprehensive weight loss peptide comparisons, see our best peptides for weight loss guide.

Long-term considerations

Maintenance dosing

After reaching goal weight:

• Some continue at therapeutic dose indefinitely

• Others may reduce to lower maintenance dose (4-8 mg)

• Weight regain is common if medication is stopped

• Long-term studies are ongoing

Duration of treatment

Based on clinical trial data:

• Weight loss continues for at least 48-68 weeks

• Plateau may not occur even at 48 weeks

• Long-term (multi-year) data not yet available

• Treatment may be indefinite for weight maintenance

Monitoring recommendations

Regular check-ins should include:

• Weight and body composition

• Blood pressure and heart rate

• Blood glucose and HbA1c

• Lipid panel

• Liver and kidney function

• Review of symptoms and side effects

Frequently asked questions

What is the starting dose for retatrutide?

The standard starting dose is 2 mg once weekly, based on Phase 2 and Phase 3 clinical trials. Some protocols may start at 1 mg, but 2 mg is most common. Starting low minimizes side effects and allows the body to adapt.

How often should I increase my retatrutide dose?

Dose increases typically occur every 4 weeks, following the clinical trial schedule. However, if you're experiencing significant side effects, you should hold at your current dose for an additional 2-4 weeks before attempting to increase.

What is the maximum dose of retatrutide?

The maximum dose studied in clinical trials is 12 mg weekly. However, many people achieve excellent results at 8 mg, and the maximum dose isn't necessary or appropriate for everyone. Work with your provider to find your optimal dose.

How much weight can I expect to lose?

In Phase 2/3 trials, participants lost an average of 24-29% of body weight at the highest doses over 48-68 weeks. Results vary based on individual factors, lifestyle, and adherence.

What if I miss a dose?

If less than 4-5 days have passed since your scheduled injection, take the dose as soon as you remember. If more than 5 days have passed, skip the missed dose and resume your normal schedule the following week. Never double up on doses.

Can I split my weekly dose into multiple injections?

This is not typically recommended, as clinical trials used once-weekly dosing. However, if your calculated volume exceeds 1 mL, you may need to split the dose into two injection sites during the same administration.

How long should I stay on retatrutide?

Duration depends on individual goals and response. Clinical trials lasted 48-68 weeks, with ongoing weight loss throughout. Many may need long-term or indefinite treatment to maintain weight loss. Discuss with your provider.

What should I do if side effects are severe?

If side effects are severe, contact your healthcare provider immediately. You may need to hold your current dose, reduce to a previous lower dose, or consider additional supportive medications. Never try to "push through" severe symptoms.

Is the dosing the same for men and women?

Clinical trials used the same dosing for both men and women. However, women may experience stronger appetite suppression effects and may benefit from slower titration in some cases.

How should I store reconstituted retatrutide?

Store reconstituted retatrutide refrigerated at 2-8°C (35.6-46.4°F). Use within 2-4 weeks of reconstitution. Keep away from light. Never freeze reconstituted solution.

The bottom line on retatrutide dosing

Proper dosing is fundamental to retatrutide success. The clinical trial data is clear:

Key principles:

• Start at 2 mg weekly

• Increase by one dose level every 4 weeks

• Hold if side effects are significant

• 8-12 mg is the typical maintenance range

• Slower is better than faster

Remember:

• This medication is investigational and not FDA-approved

• Work with a qualified healthcare provider

• Individualize based on your response

• Patience during titration pays off

For more information on retatrutide and related peptides, explore our related guides below.

Related guides

• GLP-3 peptide guide – Understanding retatrutide's mechanism

• Best peptides for weight loss – Comprehensive options

• Peptide dosage calculator – Accurate measurements

• How to reconstitute peptides – Preparation guide

• Peptide storage guide – Keeping peptides stable

• Peptide safety guide – Understanding risks

• Getting started with peptides – Beginner's introduction

• Semaglutide dosage guide – Comparing protocols

• Peptides for blood sugar – Metabolic support

• BPC-157 guide – GI support peptide

In case I don’t see you, good afternoon, good evening, and good night. Take care of yourself. <3