Injecting a Weight Loss Pen: Where, How and Storage

You can inject a weight loss pen at home, provided the medication was prescribed by your doctor and you have been taught the technique at the clinic. Usable sites are the subcutaneous fat of the abdomen, the front of the thigh and the outer upper arm — injecting once weekly on the same day, rotating the site each time.

Can you inject it yourself, and what can’t you do yourself?

This class of medication comes as a prefilled pen precisely so patients can administer it at home. Self-injection is therefore a normal part of treatment, not a workaround.

What cannot be done yourself is everything before that: assessing whether the medication suits you, choosing the starting dose, setting the schedule for increases, and deciding whether to continue or stop. These are your doctor’s decisions after history-taking and assessment, because this class is a specially controlled drug under Thai law.

In practice at the clinic, people starting treatment are shown how to use the pen, how to store it, and how to dispose of needles before going home to inject. If any step is unclear, you can ask for a repeat demonstration before you leave.

Where can you inject?

This medication goes into the subcutaneous fat layer — not into muscle and not into a vein. Three areas are used:

• The abdomen, keeping about 5 cm clear of the navel. This is the most commonly used site because it is easy to reach and has a fat layer beneath.
• The front of the thigh, toward the middle and slightly outward.
• The outer upper arm, which usually needs someone else to help because the angle is awkward.

Avoid skin that is bruised, broken, inflamed or reddened, areas with varicose veins, spots with hard lumps from repeated injections, and areas with pronounced stretch marks.

Why rotate the site?

Injecting repeatedly into the same spot can alter the subcutaneous fat tissue there, producing hard lumps or dents. Beyond appearance, altered tissue may also make absorption less consistent.

The usual approach is to rotate weekly — alternating left and right, or between abdomen and thigh — and to keep a reasonable distance from the previous injection point. Some people note it down or photograph it so they remember where they injected last week.

The general injection sequence

The steps below give the order of operations. They do not replace the package insert or the instructions your clinic gave you, and you should always follow the guidance specific to your pen.

1. Wash your hands and check the medication name, dose and expiry date on the pen
2. Inspect the medication — the solution should look as it should, not cloudy, without particles, and never previously frozen
3. Choose a site different from last week, wipe with alcohol and let it dry
4. Inject as directed for your pen model, holding for the specified time so the full dose is delivered
5. Put the needle straight into a sharps container — do not re-cap it
6. Record the date and site to plan the following week

If there is slight bleeding after withdrawing the needle, press gently with clean cotton wool. Do not massage the injection site.

How to store the medication

This class of medication is temperature-sensitive. The general principle is to refrigerate at the temperature stated on the label, never freeze, and never use it if you suspect it has been frozen. Keep it away from light and avoid the fridge door, where temperature fluctuates most.

If the medication must leave the fridge — when travelling, for example — the package insert for each product specifies acceptable temperatures and durations. Read the documentation you received or ask the clinic rather than estimating, because medication stored at the wrong temperature can degrade while still looking normal.

This is another reason not to buy from sources of unknown origin: there is no way to verify how the product was kept in transit.

Precautions and symptoms to report

• Do not double the dose to make up a missed injection — follow the instructions given when the medication was dispensed
• Do not adjust the dose yourself, up or down, as it affects both safety and treatment outcome
• Never share a pen or needle with anyone, even after changing the needle
• Tell your doctor about hard lumps, swelling, redness or significant pain at the injection site that does not settle
• Contact your doctor immediately for severe persistent abdominal pain, vomiting to the point of dehydration, or an allergic reaction

Getting started at the clinic

At Onnyx Clinic the process starts with seeing a doctor to assess whether the medication suits your health. The doctor then sets the starting dose and explains the follow-up plan. The clinic stocks 2.5 mg pens as the starting dose and 5 mg as prescribed. Mounjaro pens start at 2,499 THB.

Before you leave you will receive guidance on using the pen, storing it and disposing of needles, with a repeat demonstration available if you are not yet confident. Consult a doctor at Onnyx Clinic or ask via LINE: @onnyxclinic

References

• How should Mounjaro (tirzepatide) doses be increased in adults? (Lilly Medical)
• Tirzepatide Once Weekly for the Treatment of Obesity — SURMOUNT-1 (NEJM)
• Gastrointestinal tolerability of tirzepatide in SURMOUNT-1 to -4 (Diabetes, Obesity and Metabolism)
• Thai Food and Drug Administration — drug product database