Where to Inject Testosterone, Semaglutide and Mounjaro: A Practical Guide

Self-injecting medication for the first time can feel daunting. Most people feel a bit anxious about it, and that's completely normal. The good news is that once you've done it a handful of times, it becomes second nature. This guide covers the most common self-injectable medications used in the UK right now: testosterone (for TRT), semaglutide (Wegovy and Ozempic), and Mounjaro (tirzepatide). Whether you've just been prescribed one of these or you're still weighing up your options, understanding where and how to inject will help you feel a lot more confident.

Subcutaneous vs intramuscular: what's the difference?#

Before getting into specific sites, it helps to understand the two main injection methods you'll encounter.

Subcutaneous injections go into the fatty tissue just under the skin. This is the method used for semaglutide (Wegovy and Ozempic) and Mounjaro, and increasingly for testosterone too. Absorption is slower and more gradual, which suits medications that need a steady release over time.

Intramuscular injections go deeper, into muscle tissue. Traditional testosterone injections use this method. Absorption is generally faster, though some testosterone formulations are specifically designed for the slower subcutaneous route.

Knowing which method applies to your medication matters, because the injection site, needle length and technique all differ between the two.

Where to inject testosterone#

Testosterone can be given either intramuscularly or subcutaneously, depending on the formulation and the clinical recommendation you receive. Here's a breakdown of the main options.

Glutes (intramuscular)#

The gluteal muscles (your buttocks) are the most commonly used site for intramuscular testosterone. There's plenty of muscle mass here, it's well away from major nerves and blood vessels when you inject correctly, and most people find it the least uncomfortable option.

Use the upper outer quadrant of the buttock. Insert the needle below the level of your pelvis, angling away from your spine. A 25G or 27G needle, around 1 inch in length, works well for most people, though needle length should be adjusted based on body size.

Thigh (intramuscular)#

The quadriceps (front of the thigh) are a practical alternative, particularly if you struggle to reach your glutes. Inject into the middle-outer section of your upper thigh. This site is easy to access when injecting yourself and has a good muscle mass. Use a similar needle gauge to the glute (25G or 27G, 1 inch).

Abdomen (subcutaneous)#

Subcutaneous testosterone injections into the abdomen are becoming more widely recommended. Research suggests this route produces a smoother, more stable testosterone release with fewer peaks and crashes compared to intramuscular injection. This can reduce side effects like mood fluctuations and haematocrit rises.

Use a finer needle for subcutaneous injections: 27G or 29G, with a shorter length (typically 0.5 inches). Inject into the fatty tissue at least 5 cm away from your navel, pinching the skin gently before inserting.

Shoulder/deltoid (intramuscular)#

Some men use the deltoid muscle in the upper arm. It's less popular among clinicians because it's a smaller muscle with less margin for error. There's a higher risk of hitting a nerve or blood vessel here compared to the glute or thigh, so it's generally not recommended unless you've been specifically shown this technique by a healthcare professional.

Sites to avoid#

Never inject into skin that is bruised, scarred, inflamed or infected. Avoid areas where you've recently injected until the site has fully recovered. Don't inject into varicose veins or areas of broken skin. If you're ever unsure whether a site looks suitable, err on the side of caution and choose a different location.

How often should you inject testosterone?#

This depends on the testosterone ester you're using. Testosterone enanthate and cypionate are typically injected once or twice weekly. Testosterone propionate has a shorter half-life and may require more frequent dosing. Testosterone undecanoate (Nebido) is a longer-acting formulation given every 10 to 14 weeks by a clinician. Your prescriber will give you a specific schedule based on your formulation and blood test results.

Some TRT users on twice-weekly injections prefer smaller, more frequent subcutaneous doses into the abdomen. This approach tends to produce stable hormone levels and is particularly popular among those who are sensitive to testosterone fluctuations.

If you're considering TRT and want to understand your options, Totiva offers pharmacist-led online consultations and can guide you through the process from blood testing through to prescription.

Where to inject semaglutide (Wegovy and Ozempic)#

Semaglutide is a subcutaneous injection, meaning it goes into the fatty tissue under the skin rather than into muscle. Both Wegovy and Ozempic use pre-filled auto-injector pens that make the process straightforward.

The three approved injection sites are:

• Abdomen: At least 5 cm away from the navel. This is the most commonly used site and is easy to access.
• Thigh: The front or outer upper thigh, where there is enough subcutaneous fat beneath the skin.
• Upper arm: The back of the upper arm. This site often requires a second person to assist unless you have good flexibility.

There is no clinically meaningful difference in how semaglutide is absorbed between these three sites, so choose whichever you can access most comfortably and consistently.

How to inject Wegovy or Ozempic#

1. Wash your hands thoroughly with soap and water.
2. Remove the pen from the fridge and allow it to come to room temperature for around 15 to 30 minutes. Injecting cold medication can sting more.
3. Check the pen: make sure the liquid is clear and colourless, and that the expiry date has not passed.
4. Select your injection site and clean it with an alcohol swab. Allow it to dry fully before injecting.
5. Remove the pen cap and attach a new needle if your pen requires one. Most auto-injectors (including Wegovy) have a built-in needle.
6. Pinch the skin gently at the injection site and press the pen firmly against the skin.
7. Activate the injection as directed in your pen's instructions (usually by pressing a button) and hold the pen in place for the required count (typically 5 to 10 seconds).
8. Remove the pen, release the skin and dispose of the pen safely in a sharps container.

Weekly semaglutide injections can be taken on any day, but keep it consistent: the same day each week, at roughly the same time. You don't need to take it with food.

If you're looking at semaglutide for weight loss and want to explore whether it's right for you, Totiva provides online weight loss consultations with UK-registered pharmacists.

Where to inject Mounjaro (tirzepatide)#

Mounjaro uses the same subcutaneous injection method as semaglutide. The approved sites are identical: abdomen (avoiding 5 cm around the navel), front or outer thigh, or the back of the upper arm.

Mounjaro comes in a pre-filled auto-injector pen. The technique is very similar to Wegovy: wash your hands, allow the pen to reach room temperature, clean the site, pinch the skin, press and hold for a full count before removing.

One practical difference worth noting is that the Mounjaro pen uses a slightly different activation mechanism to Ozempic/Wegovy pens. Always read the specific instructions that come with your pen, since the steps for checking, priming and injecting vary slightly between brands.

Like semaglutide, Mounjaro is given once weekly and does not require food. If you miss a dose, you can take it within four days of the missed dose. If more than four days have passed, skip that dose and resume your normal weekly schedule.

For more information on Mounjaro and other weight loss injections available in the UK, take a look at Totiva's weight loss service.

Rotating injection sites: why it matters#

Rotation is one of the most important habits to build with any injectable medication.

Using the same spot repeatedly causes the fatty tissue to harden over time, a condition called lipohypertrophy. Once this occurs, absorption becomes erratic and unpredictable, which can affect how well your medication works. You might notice lumps, numbness or thickening at a favourite site.

A simple rotation system helps:

• Divide each injection area into zones (for example, left and right sides of the abdomen, and left and right thighs).
• Move at least 2 to 3 cm from your previous injection point each time.
• Keep a note in your phone or use a simple tracker to remember where you last injected.
• Allow each site to recover fully before returning to it. With once-weekly injections, this is straightforward.

If you notice a lump or hardened patch, avoid that area until it resolves. This can take several weeks to months.

Injection technique tips for different body types#

This is something most guides overlook, but it genuinely matters.

Lower BMI or less subcutaneous fat: Use a shorter needle (0.5 inches or 4 mm for subcutaneous injections) and pinch the skin firmly to gather enough tissue. Injecting at a 45-degree angle can help ensure you stay in subcutaneous tissue rather than inadvertently going intramuscular.

Higher BMI: You may have more subcutaneous tissue, which is generally fine. Injection at 90 degrees is usually appropriate. The key is ensuring the needle reaches the fatty layer and doesn't stay in the dermis.

Older or thinner skin: Skin elasticity decreases with age, and subcutaneous tissue can become less forgiving. Gentle pinching and careful site rotation are especially important. If you notice bruising more easily, discuss this with your prescribing pharmacist or GP.

Managing injection site reactions#

Mild redness, itching or a small raised bump at the injection site is common, especially when you first start. These usually resolve within a day or two and are not a cause for concern in most cases.

More significant reactions, such as persistent swelling, spreading redness, pain lasting several days or any signs of infection (warmth, discharge, fever), should be reviewed by a clinician. Don't inject into a site that looks infected.

If you experience a widespread allergic reaction (hives, difficulty breathing, swelling of the face or throat) after any injection, seek emergency medical attention immediately. Severe allergic reactions to GLP-1 medications are rare, but they do occur.

For GLP-1 medications like Wegovy, Ozempic and Mounjaro, you can report side effects to the MHRA via the Yellow Card scheme.

Sharps disposal in the UK#

This is a legal responsibility, not just good practice. You cannot put needles or pen devices in your household recycling or general rubbish.

Your options in the UK:

• NHS sharps bin: Ask your GP surgery, pharmacist or local council about the free sharps bin collection scheme. Many areas offer a home collection service or drop-off points at pharmacies.
• Local council collection: Contact your local authority, as provision varies. Many councils run clinical waste collection services for residents on long-term injectable medications.
• Pharmacy return: Some pharmacies accept filled sharps bins for safe disposal.

Always fill your sharps bin to no more than two-thirds capacity before sealing and disposing of it.

A note on NHS vs private prescriptions#

In the UK, testosterone replacement therapy is available on the NHS, but waiting times for specialist endocrinology or urology referrals can be lengthy. Many men are now accessing TRT through regulated private services, which can offer faster consultations and ongoing monitoring.

Semaglutide (Wegovy) is available on the NHS for eligible patients via specialist weight management services, but access remains limited due to supply pressures and referral criteria. Mounjaro (tirzepatide) received NICE approval for weight management, and NHS rollout is ongoing, though currently limited.

Private prescription services like Totiva operate under GPhC regulation, offering the same clinical standards as NHS prescribing with greater flexibility and speed. If you're considering starting weight loss medication, you can begin a consultation here.

When to speak to a clinician#

Self-injection is safe when done correctly, but there are situations where you should contact your prescriber or a healthcare professional:

• Persistent or worsening injection site reactions
• Difficulty finding suitable injection sites due to lipohypertrophy
• Uncertainty about whether you injected correctly (for example, if the medication leaked)
• Any systemic symptoms after injecting: chest tightness, difficulty breathing, severe dizziness
• Blood in the syringe when you aspirate (if using manual technique for IM testosterone)

Your prescribing pharmacist or GP can also refer you to a practice nurse for a practical demonstration if you'd prefer hands-on support before injecting at home.