How GLP-1 Injections Work: A Complete Guide to Your First Self-Injection

How GLP-1 Injections Work: A Complete Guide to Your First Self-Injection

If your doctor has recently prescribed a GLP-1 injection — or you're considering one — you probably have questions beyond "will it work?". How exactly does it change what happens in your body? What does the injection itself feel like? Where do you inject? How do you not mess it up?

This guide answers all of those questions, starting with the biology and ending with a practical walkthrough you can use at home.

What Is a GLP-1, and What Does It Actually Do?

GLP-1 stands for glucagon-like peptide-1 — a hormone your gut naturally produces within minutes of eating a meal. Your small intestine releases it in response to incoming food, and it sends a cascade of signals throughout your body.

Here's what those signals do:

In the pancreas: GLP-1 stimulates the beta cells to release insulin in proportion to the glucose arriving from your meal. It also suppresses glucagon — the hormone that raises blood sugar when you haven't eaten — which helps keep post-meal glucose stable. This is called a glucose-dependent mechanism, which is why GLP-1 medications carry a very low risk of hypoglycaemia in people without diabetes.

In the stomach: GLP-1 slows gastric emptying. Food leaves your stomach more slowly and moves through the digestive tract at a reduced pace. The result: you feel full for longer after eating, and the glucose from your meal enters your bloodstream more gradually.

In the brain: GLP-1 receptors are expressed in the hypothalamus — the brain's control centre for hunger, satiety, and reward. Activating these receptors reduces appetite, lowers the perceived reward value of food, and increases the sense of fullness (Drucker DJ, Cell Metab 2018;27:740–756; Blundell J et al., Diabetes Obes Metab 2017;19:1242–1251). Patients commonly report that their relationship with food feels fundamentally different on treatment — cravings diminish, and smaller portions feel genuinely satisfying.

Naturally, GLP-1 has a problem: your body degrades it within 1–2 minutes. The hormone is rapidly broken down by an enzyme called dipeptidyl peptidase-4 (DPP-4), which means its natural effect is brief. GLP-1 receptor agonist medications are engineered to be resistant to this degradation — their half-lives range from hours (liraglutide) to days (semaglutide), enabling once-daily or once-weekly dosing.

Semaglutide: The GLP-1 Medication Prescribed for Weight Management

The most widely prescribed GLP-1 medication for weight management is semaglutide, available in Singapore as a prescription-only medicine. The key clinical evidence comes from the STEP 1 trial (Wilding et al., N Engl J Med 2021;384:989–1002) — a randomised, double-blind study in 1,961 adults with obesity or overweight with at least one weight-related condition. Over 68 weeks, participants on semaglutide 2.4 mg achieved a mean body weight reduction of 14.9% (approximately 15.3 kg), compared to 2.4% in the placebo group. More than 50% of participants lost ≥15% of body weight — a level of weight loss previously associated only with bariatric surgery.

Semaglutide is administered as a once-weekly subcutaneous injection. It is not an insulin injection. It is not chemotherapy. It is a small-volume injection using an ultra-fine needle into fatty tissue — and for most patients, the fear of injecting outweighs the reality.

Your First Self-Injection: A Practical Walkthrough

Before your first injection, your prescribing doctor or clinical team should walk you through the process. The steps below reflect general best practice and are not a substitute for individual medical guidance.

1. Prepare your supplies

You'll need:

• Your prescribed GLP-1 pen device (e.g., the FlexTouch or similar auto-injector)
• An alcohol swab
• A sharps disposal container (available at most pharmacies)
• A clean surface and clean hands

Check the pen: confirm the medication is clear and colourless (not cloudy, discoloured, or containing particles). Check the expiry date. For semaglutide, the pen is pre-filled — you do not need to mix or draw up medication.

2. Choose your injection site

The three approved subcutaneous injection sites are:

• Abdomen — at least 5 cm away from your navel (most commonly used, easiest access)
• Upper thigh — outer aspect of either thigh
• Upper arm — outer aspect of the upper arm (usually requires assistance for self-injection)

Rotate sites each week — avoid injecting into the same spot repeatedly, as this can cause lipodystrophy (hardened fatty tissue under the skin). Many patients keep a simple log or rotate clockwise around their abdomen.

3. Clean and prepare the site

Wipe the chosen site with an alcohol swab. Let it air-dry for a few seconds — injecting through wet skin can sting slightly. Do not rub the area after cleaning.

4. Administer the injection

With most auto-injector pens:

• Remove the cap
• Press the pen firmly and flat against the skin
• Press the injection button — you'll hear or feel a click as the needle deploys and the medication is delivered
• Hold the pen in place for the full count specified in your device instructions (typically 5–10 seconds) to ensure the full dose is delivered
• Remove the pen. You may see a small drop of blood or medication at the site — this is normal.

Do not recap the needle. Dispose of it in your sharps container immediately.

5. After the injection

You can gently press a clean swab against the site if there is minor bleeding, but do not rub. You may experience mild redness, minor itching, or a small bruise at the injection site — these are common and typically resolve within 24–48 hours.

The injection itself is usually not painful. The needle is very fine (typically 32 gauge) and very short. Most patients describe it as a slight pressure or nothing at all. If you experience significant pain, the needle may have hit a blood vessel — withdraw, apply pressure, and choose a different site next time.

Dose Escalation: Why You Start Low and Work Up

GLP-1 medications use a dose escalation schedule — you begin at a low dose and increase gradually over several weeks. This is not because the lower dose is therapeutic; it's a strategy to minimise gastrointestinal side effects (nausea, vomiting) while your body adjusts.

For semaglutide 2.4 mg (the weight management dose), a typical escalation schedule runs over 16 weeks:

• Weeks 1–4: 0.25 mg once weekly
• Weeks 5–8: 0.5 mg once weekly
• Weeks 9–12: 1.0 mg once weekly
• Weeks 13–16: 1.7 mg once weekly
• Week 17 onwards: 2.4 mg once weekly (maintenance)

Do not skip ahead in the escalation schedule without your doctor's advice, even if you feel you're tolerating the medication well. The escalation exists for physiological reasons, not just as a precaution.

What to Expect in the First Weeks

Week 1–2: You may notice reduced appetite sooner than you expect. Some patients report nausea, particularly in the day or two after injection. Eat small, low-fat meals. Avoid rich or fried food, which is harder to digest with slowed gastric emptying.

Week 3–8: The dose escalation continues. Nausea typically peaks and then subsides as your body adapts. Most patients see meaningful weight reduction beginning in this window. Fatigue or mild digestive disruption (constipation or loose stools) is common early on.

Week 8 onwards: For most patients, side effects have settled significantly by this point. Appetite suppression is sustained. Weight loss continues. Many patients report that their relationship with food — particularly cravings and emotional eating — has changed noticeably.

Keep all follow-up appointments with your prescribing doctor. Blood pressure, pulse, and relevant labs may be monitored, and your dose will be adjusted on schedule.

Storage and Handling

• Store unused pens in the refrigerator (2°C–8°C). Do not freeze.
• Once in use, a pen may be stored at room temperature (up to 30°C) for up to 4 weeks (check your specific product's instructions).
• Protect from direct light and heat. Do not leave pens in a car or exposed to sunlight.
• If medication has been frozen accidentally, do not use it — contact your provider.

When to Contact Your Doctor

Seek medical advice promptly if you experience:

• Severe and persistent abdominal pain (particularly if radiating to the back — a potential sign of pancreatitis)
• Persistent vomiting or inability to keep fluids down
• Signs of severe allergic reaction (rash, swelling of face/lips/throat, difficulty breathing)
• Rapid heartbeat at rest
• Vision changes

These are rare, but they are documented risks that warrant prompt clinical review.

Getting Started: Is a GLP-1 Injection Right for You?

GLP-1 medications like semaglutide are prescription-only for good reason — they're effective, but they require medical oversight, a proper eligibility assessment, and ongoing monitoring. They are not over-the-counter supplements or lifestyle products.

If you meet the eligibility criteria (typically BMI ≥ 30 kg/m², or ≥ 27 kg/m² with a weight-related condition), a telehealth consultation is the most convenient starting point.

Start your consultation at ofnoah.sg — speak with a licensed doctor, get assessed for eligibility, and if appropriate, begin treatment with full clinical support. No clinic queues. Medication delivered to your door.

This article is for educational purposes only. It does not constitute medical advice. GLP-1 medications are prescription-only medicines in Singapore. Eligibility, dosing, and suitability must be determined by a licensed physician.