Injecting safely - technique, sites, rotation

The GLP-1 pens (Wegovy and Mounjaro) are subcutaneous injection devices. The needle is short, thin, and hidden inside the mechanism so you never see it. If you have injection anxiety, knowing in advance that you will not see the needle often helps significantly.

This article covers the practical details that reduce pain, avoid problems, and make the weekly injection automatic after the first two or three weeks.

What the pen does

Both Wegovy and Mounjaro come as pre-filled, single-use disposable pens. The Wegovy pen is a FlexTouch design with a single dose per pen. The Mounjaro KwikPen is similar. Each pen delivers one weekly dose.

To inject: remove the cap, press the needle end firmly against the skin at 90 degrees, press and hold the button, count the required seconds (5-10 depending on pen and dose), release the button, withdraw the pen, replace the cap, dispose of the whole pen in a sharps bin.

The three valid injection sites

Abdomen: the front of your abdomen, at least 2 inches away from your belly button. Usually the easiest site for self-injection because you can see what you are doing clearly.

Thigh: the front or outer side of the upper thigh. Useful if abdominal fat is minimal or if you have had previous abdominal surgery.

Upper arm: the back of the upper arm. Harder to self-inject because reach and angle are awkward. Easier if someone else is injecting for you.

All three sites absorb the medication at similar rates.

How to rotate sites

You should not inject into the same spot week after week. Repeated injection at the same site leads to lipohypertrophy: fatty lumps that become slower to absorb and uncomfortable over time.

The rule we teach patients:

Pick two sites you will use (e.g. left and right sides of abdomen).

Alternate between them each week.

Within each site, move at least one inch from the previous injection location.

Avoid injecting into scar tissue, stretch marks, or areas of broken skin.

Avoid injecting within 2 inches of your belly button.

A simple record: mark the week and site on a small sticker or in a phone note. Most patients develop a pattern within 2-3 months and no longer need to record.

Pen storage

Before first use: store in the fridge at 2-8°C. Do not freeze. Do not store above 30°C.

After first use (if you start using a pen mid-week for any reason): store at room temperature for up to 6 weeks. Do not refrigerate once you have started using a pen.

Wegovy and Mounjaro single-use pens are one-dose-and-discard, so after-first-use rules rarely apply in practice.

Before injecting, take the pen out of the fridge 20-30 minutes beforehand. Injecting cold medication is significantly more painful than injecting medication at room temperature.

Technique: minimising pain

The injection itself is mild for most people, often less painful than a fingerprick blood test. A few specific things reduce discomfort further.

Room temperature medication. Cold injections hurt more.

Firm pressure against the skin before activating the pen. The needle enters more cleanly.

Quick, decisive activation. Hesitation causes the pen to depress unevenly.

Hold the pen in place for the full counted time. Releasing early reduces delivered dose and can cause leakage at the injection site.

Pinch the skin if you have very little subcutaneous fat. This lifts the fat layer away from the muscle and ensures you inject into the correct layer.

Do not massage the site afterwards. Massaging can affect absorption and worsen bruising.

What is normal after injection

Small red dot at the injection site. Fades within 1-2 hours.

Mild stinging or warmth for 30-60 seconds after the pen is withdrawn. Normal.

Small drop of fluid at the injection site. Rarely means a significant dose was lost.

Small bruise sometimes appears 24-48 hours later. Normal; usually caused by a small blood vessel being nicked.

What is not normal

Significant swelling (more than 2cm diameter) or persisting beyond 48 hours.

Severe pain at the injection site (different from stinging).

Pus or crusting (suggesting infection).

A lump that does not go away over a week (lipohypertrophy has started).

A lump that throbs, is red-hot, or accompanied by fever (possible cellulitis).

Message us if any of these. Straightforward fixes usually - different site, treating any skin infection, adjusting needle depth.

Disposing of pens

Used pens are sharps waste. They cannot go in regular household rubbish, recycling, or the bathroom bin.

UK options:

Request a sharps bin from us when you start treatment (included at no extra cost). We collect full bins at your monthly review.

Request a sharps bin from your NHS GP. Some surgeries will supply them.

Buy a small-volume sharps bin from any UK pharmacy (~£5-10).

Never put a used pen in the washing machine, do not attempt to recycle.

Injection anxiety

This is real and common. About 10 percent of patients have significant needle phobia.

If you have been unable to self-inject in the past, three approaches that help:

In-person assessment. We teach injection technique during your Westfield consultation and do your first injection with you there.

Partner-injection. If someone else (partner, close friend, sibling) can do the injection for you, that is a legitimate approach.

Telehealth coaching. Video call with our nurse while you do your first injection yourself, using breathing and pacing techniques.

If none of these work, Rybelsus (oral semaglutide) is a real option, though the weight-loss effect is less.

The honest bottom line

Injection technique is a minor hurdle that disappears after the first two or three weekly injections. By week 4 most patients say the injection itself is the least thought-about part of the treatment.

Ready to start?

If this article has made you think medication might help, the next step is a short consultation with one of our weight-management doctors.

Begin your consultation at this link. Online in 30 minutes, or in person at Westfield London.