Mounjaro Dosing & Usage Guide UK 2025

Last Updated: December 28, 2025 | Source: Eli Lilly UK, MHRA Patient Information Leaflet

Mounjaro is a once-weekly subcutaneous injection that comes in a pre-filled, single-dose pen. Proper injection technique, following the recommended titration schedule, and understanding storage requirements are essential for safety, tolerability, and optimal weight-loss results. This comprehensive guide covers everything you need to use Mounjaro correctly.

💉 Step-by-Step Injection Instructions

Follow these detailed steps for safe, effective Mounjaro administration:

Before You Begin (Preparation):

1. Wash hands thoroughly with soap and water for 20+ seconds; dry completely
2. Gather supplies:
   • Mounjaro pen (check expiry date and that solution is clear/colourless)
   • Alcohol wipe (70% isopropyl alcohol)
   • Sharps disposal container (rigid, puncture-proof container)
   • Cotton wool or gauze (optional, for post-injection pressure)
3. Remove pen from refrigerator 30-60 minutes before injection to reach room temperature (reduces injection discomfort)
4. Inspect the pen:
   • Solution should be clear and colourless (no particles, cloudiness, or discolouration)
   • Do NOT use if solution appears cloudy, coloured, or contains particles
   • Check dose window shows correct dose (2.5, 5, 7.5, 10, 12.5, or 15mg)
5. Choose injection site (see site selection section below)

Injection Process (Step-by-Step):

1. Select and clean injection site:
   • Abdomen (5cm away from belly button), front of thighs, or upper arms
   • Clean site with alcohol wipe using circular motion
   • Allow to air dry completely (30-60 seconds)—do NOT blow on it
2. Remove pen cap by twisting anti-clockwise—you should hear a click (do NOT pull straight off)
3. Check the needle:
   • Needle should automatically extend when cap is removed
   • A drop of liquid at needle tip is normal
4. Position the pen:
   • Hold pen at 90-degree angle to skin (perpendicular)
   • Do NOT touch the needle or allow it to contact any surface
5. Pinch injection site (optional but recommended for thinner individuals):
   • Gently pinch 2-3cm of skin between thumb and forefinger
   • Creates a “cushion” ensuring subcutaneous (not intramuscular) injection
6. Insert needle firmly by pressing pen straight down against skin:
   • Needle penetrates automatically—you may feel slight pressure
   • Hold pen steady against skin
7. Press and hold the injection button:
   • Press grey button on end of pen firmly
   • Hold for 10 seconds minimum (count: “1 Mississippi, 2 Mississippi…” to 10)
   • You’ll hear two clicks: first click starts injection, second confirms completion
   • Do NOT release button until 10 seconds have elapsed after second click
8. Remove pen from skin:
   • Lift pen straight away from injection site
   • Needle retracts automatically into pen
9. Check dose delivery:
   • Look at dose window—should show “0” if full dose delivered
   • If dose window shows a number other than 0, contact your prescriber (partial dose delivered)
10. Dispose of pen immediately in sharps container:
    • Do NOT recap the pen
    • Place entire pen in puncture-proof sharps container
    • Mounjaro pens are single-use only—never reuse
11. Apply pressure if needed:
    • If injection site bleeds, apply cotton wool/gauze with gentle pressure for 30 seconds
    • Small amount of bleeding or bruising is normal

📍 Injection Site Selection & Rotation

Proper injection site selection and rotation prevents tissue irritation, improves absorption, and reduces injection site reactions.

Approved Injection Sites:

• Abdomen (belly): Most common site; fastest absorption
  • Area: Entire abdomen EXCEPT within 5cm of belly button
  • Avoid: Belt line, any areas with scars, moles, or skin irritation
  • Best for: Most patients; easy to self-inject
• Thighs (front/outer): Alternative site; slightly slower absorption
  • Area: Front and outer thigh, between hip and knee
  • Avoid: Inner thigh, areas close to groin
  • Best for: Those who prefer leg injection or have limited abdominal space
• Upper arms (back): Least common; requires assistance
  • Area: Back of upper arm, between shoulder and elbow
  • Limitation: Difficult to self-inject; usually requires help from another person
  • Best for: When abdomen and thighs are unavailable

Site Rotation Schedule:

Rotate injection sites with each weekly dose to prevent lipohypertrophy (tissue hardening) or lipoatrophy (tissue breakdown):

• Week 1: Left abdomen (lower)
• Week 2: Right abdomen (lower)
• Week 3: Left abdomen (upper)
• Week 4: Right abdomen (upper)
• Week 5: Left thigh
• Week 6: Right thigh
• Week 7: Return to Week 1 pattern

Site Selection Considerations:

• Never inject into: Areas with bruising, scars, moles, tattoos, stretch marks, redness, or skin irritation
• Maintain 3cm spacing: Each injection should be at least 3cm away from previous injection site
• Avoid recently exercised areas: Wait 2-3 hours after exercise before injecting in that area (exercise increases blood flow, potentially affecting absorption)
• Temperature consideration: Cold skin constricts blood vessels; room temperature skin improves comfort and absorption

📊 Understanding Mounjaro Dosages

Mounjaro is available in six different strengths (2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, and 15mg), allowing prescribers to tailor treatment to individual needs and tolerance. Dosing typically starts low and may increase gradually over time—a process called titration.

Why Doses Vary Between Patients

Prescribing decisions depend on multiple factors, and no two journeys are identical. Your prescriber may consider:

• Individual tolerance: Some people respond well to lower doses; others may need higher strengths for optimal benefit
• Side effect management: Progression may slow or pause if gastrointestinal symptoms need time to settle
• Treatment goals: Weight management targets, blood sugar control (if diabetic), and overall health objectives
• Response to current dose: If a dose is working well, staying at that level may be appropriate
• Personal circumstances: Cost, lifestyle factors, and patient preference all play a role

General Dosing Patterns (Not Rules)

While prescribing varies, many UK clinicians follow a gradual approach:

• Starting dose: Typically 2.5mg for the first 4 weeks to allow the body to adjust
• Gradual increases: Doses may increase every 4 weeks if tolerated and clinically appropriate
• Flexible timelines: Some people progress faster or slower; there is no “correct” speed
• Staying at lower doses: Not everyone needs to reach 15mg—many achieve excellent results at 5mg, 7.5mg, or 10mg
• Maximum dose: 15mg is the highest licensed strength; progression stops here regardless

What to Discuss with Your Prescriber

Before starting or changing doses, consider asking:

• What dose are you recommending for me, and why?
• How will we know if this dose is working?
• What side effects should I watch for, and when should I contact you?
• When might we consider increasing, decreasing, or staying at this dose?
• What happens if I experience significant side effects?

📚 Mounjaro Dosage Guides

Each Mounjaro dose has unique characteristics, common experiences, and practical considerations. Explore the guides below to learn more about the dose you’re currently taking or considering:

🕐 Dosing Schedule & Timing

Mounjaro is administered once weekly, same day each week. Flexibility exists, but consistency optimises results.

Choosing Your Weekly Injection Day:

• Consider side effect timing: If nausea occurs 24-48 hours post-injection, choose a day allowing rest (e.g., Friday for weekend recovery)
• Routine alignment: Pick a day with established routine (easier to remember)
• Social considerations: Some avoid weekend injections to minimise social event disruptions
• Prescriber appointments: Injecting day before consultations allows timely discussion of side effects

Injection Time of Day:

• No optimal time medically: Mounjaro works effectively regardless of injection time
• Morning injections: Allows monitoring for side effects during daytime hours
• Evening injections: Potential overnight nausea occurs during sleep (some patients find this easier)
• Consistency matters: Injecting same time each week maintains stable blood levels

Flexibility Window:

• ±2 days: If you inject Mondays, anywhere from Saturday-Wednesday is acceptable
• Beyond ±2 days: Considered a “missed dose” (see section below)
• Travel/events: Can temporarily shift injection day within flexibility window, then return to regular schedule

❌ Missed Dose Protocol

Occasionally missing a dose happens. Here’s exactly what to do based on timing:

If Less Than 4 Days Since Scheduled Dose:

• Action: Inject the missed dose as soon as you remember
• Next dose: Resume regular weekly schedule from this injection
• Example: Usually inject Mondays, forgot, remembered Wednesday → inject Wednesday, then next injection following Monday (7 days later)

If 4 Days or More Since Scheduled Dose:

• Action: Skip the missed dose entirely
• Next dose: Wait for next regularly scheduled injection day
• Do NOT double dose to make up for missed injection
• Example: Usually inject Mondays, forgot, remembered Friday (4 days later) → skip this week, inject next Monday as normal

Multiple Missed Doses (2+ Weeks):

• Action: Contact your prescriber before resuming
• Likely recommendation: Restart at lower dose (typically drop back 1-2 dose levels) to rebuild tolerance
• Reason: GI tolerance decreases after 2+ weeks without medication; resuming at full dose may cause severe nausea
• Example: Were taking 10mg, missed 3 weeks → prescriber may recommend restarting at 5mg or 7.5mg

🧊 Storage Requirements

Proper storage maintains Mounjaro potency and safety throughout its shelf life:

Unopened Pens (Before First Use):

• Refrigerate: Store at 2-8°C (fridge temperature) until ready to use
• Do NOT freeze: Never store in freezer; if accidentally frozen, discard pen (cannot be used)
• Keep in original box: Protects from light
• Expiry date: Check printed date; do not use past expiry even if refrigerated
• Storage duration: Can remain refrigerated until expiry date (typically 18-24 months from manufacture)

Opened Pens (After Removing Cap):

• Single-use only: Mounjaro pens are NOT multi-dose; entire pen is discarded after one injection
• Use immediately: Once cap is removed, inject within a few minutes
• Do NOT store after opening: Cannot re-cap; needle is exposed making storage unsafe

Room Temperature Storage (Temporary):

• Maximum duration: Can be kept at room temperature (up to 30°C) for maximum 21 days
• Use case: Useful for short travel periods without refrigeration access
• Cannot return to fridge: Once removed from refrigeration for extended period, keep at room temp and use within 21 days
• Track removal date: Note when pen left refrigeration to calculate 21-day window

Travel Considerations:

• Short trips (1-3 days): Can carry at room temperature; return to fridge upon arrival
• Longer trips: Use cooler bag with ice packs (ensure pen doesn’t contact ice directly—no freezing)
• Air travel: Carry in hand luggage (not checked baggage—temperature extremes in cargo hold); bring prescription documentation
• Hotel storage: Use minibar fridge if available; if not, store in coolest part of room away from direct sunlight

✅ Optimising Mounjaro Effectiveness

Beyond proper injection technique, these strategies maximise weight loss results:

1. Timing Considerations:

• Food timing: Can inject with or without food (no food restrictions for injection timing)
• Alcohol: Avoid alcohol on injection day (increases nausea risk; alcohol and Mounjaro both affect blood sugar)
• Other medications: Generally no timing restrictions; discuss with prescriber if taking multiple daily medications

2. Diet Optimisation:

• Protein priority: 80-120g protein daily prevents muscle loss during weight loss
• Small, frequent meals: 4-6 smaller meals better tolerated than 3 large meals
• Avoid trigger foods: Fatty, spicy, or very sweet foods worsen nausea
• Hydration: 2-3 litres water daily (Mounjaro can slow gastric emptying; adequate hydration essential)
• Fibre intake: 25-35g daily prevents constipation (common side effect)

3. Exercise Integration:

• Resistance training: 2-3 sessions weekly preserves muscle mass during weight loss
• Cardio: 150+ minutes moderate intensity weekly supports weight loss
• NEAT: Increase non-exercise activity thermogenesis (walking, stairs, standing)
• Post-injection exercise: Light activity day after injection may reduce nausea for some

4. Monitoring & Adjustments:

• Weekly weigh-ins: Same day, same time, same conditions (e.g., Thursday mornings, post-bathroom, before breakfast)
• Body measurements: Waist, hips, thighs measured monthly (sometimes inches lost without scale movement)
• Progress photos: Monthly photos from same angle/lighting show changes scale might miss
• Side effect log: Track timing and severity; helps identify patterns and triggers

🚨 When to Seek Medical Help

Contact your prescriber or seek emergency care if you experience:

Urgent (Call Prescriber Same Day):

• Persistent vomiting (unable to keep liquids down for 12+ hours)
• Severe or persistent abdominal pain
• Severe diarrhoea lasting 24+ hours
• Signs of dehydration (dark urine, dizziness, rapid heartbeat)
• Unexplained severe weakness or fatigue
• Injection site infection (redness spreading, warmth, pus, fever)

Emergency (Call 999 or Go to A&E):

• Severe allergic reaction (difficulty breathing, throat swelling, severe rash/hives)
• Severe abdominal pain radiating to back (possible pancreatitis)
• Persistent nausea/vomiting with severe abdominal pain (possible pancreatitis)
• Vision changes or eye pain (rare but requires immediate assessment)
• Symptoms of severe hypoglycaemia if diabetic (confusion, loss of consciousness, seizures)
• Chest pain, difficulty breathing, or signs of blood clot

❓ Usage FAQs

Can I switch injection sites within the same session?

No—complete full dose at one site. Switching mid-injection may result in partial dose delivery and unpredictable absorption.

What if I see air bubbles in the pen?

Small air bubbles are normal and harmless. Mounjaro pens are pre-filled and do not require air removal (unlike some multi-dose pens). Inject as normal.

Can I inject through clothing?

No—always inject into clean, bare skin. Clothing increases infection risk and may prevent complete needle insertion.

How long until Mounjaro starts working?

Blood levels stabilise after 4-5 weeks. Most patients notice appetite suppression within 1-2 weeks, with measurable weight loss by week 4-6. Peak effectiveness typically reaches by week 8-12 at each dose.

Can I split doses (e.g., inject 5mg twice weekly instead of 10mg once)?

No—Mounjaro is engineered for once-weekly dosing. Splitting doses alters pharmacokinetics and is not supported by clinical trials. Only use as prescribed: one full dose, once weekly.

What if the pen malfunctions during injection?

If you did NOT hear two clicks or dose window doesn’t show “0”, contact your prescriber immediately. Do NOT inject another full pen (risk of overdose). Your prescriber will advise whether partial dose was delivered and next steps.

Can I reuse needles between injections?

No—Mounjaro pens are single-use only. The entire pen (including needle) is discarded after one injection. Needle reuse increases infection risk and dulls needle tip (painful subsequent injections).

🎯 Key Takeaways: Using Mounjaro

• Master injection technique: 90-degree angle, hold button 10 seconds, rotate injection sites weekly

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