The TRT Basics: Why Injections?
Testosterone replacement via injection is the most common, most practical, and most cost-effective form of TRT in the UK.
Why injections over other routes?
- Stability: Injections produce stable testosterone levels (particularly with appropriate frequency)
- Cost: Cheaper than gels or patches per unit of testosterone delivered
- Simplicity: Once you're comfortable with injection, no daily application needed
- Flexibility: Easy to adjust dose, easy to discontinue if needed
This guide is for men already prescribed testosterone via injection and wanting to understand technique, protocol, and practical management.
Types of Testosterone Available in the UK
Sustanon 250
What it is: A blend of four testosterone esters (testosterone propionate, phenylpropionate, isocaproate, decanoate). The mix is designed to provide both rapid and sustained testosterone delivery.
UK availability: Widely available on NHS and private prescription.
Mechanism: Propionate and phenylpropionate are absorbed within days. Isocaproate lasts 7–10 days. Decanoate lasts 3 weeks. The idea is immediate peak plus sustained levels.
Reality: The mixture doesn't work as intended. Peak testosterone (from propionate) occurs at 24 hours, then drops rapidly. You get significant fluctuation within a week, and most men need injections every 5–7 days for stable levels.
Dose: Typically 250 mg per injection. Most men inject weekly or twice weekly.
Downsides: Frequent fluctuation (peak/trough) means some days you feel great, some days you feel worse. Inconsistent levels can worsen side effects and unpredictable mood/energy.
Practical: Sustanon can work, but requires frequent injection (weekly). If you're going to inject frequently, single-ester testosterone (below) is usually better.
Testosterone Enanthate or Testosterone Cypionate
What they are: Single-ester testosterone, both with an 8–10 day half-life. These are interchangeable for practical purposes.
UK availability: Enanthate is most common on NHS. Cypionate is more available privately.
Mechanism: Predictable, steady release over 7–10 days. Peak at 24–48 hours, then gradual decline.
Dose: Typically 100–200 mg per injection.
Injection frequency: Weekly (most common) or every 10–14 days (if dosing higher — e.g., 200 mg every 14 days).
Why preferred: Stable levels, less frequent injection than Sustanon, better predictability of how you feel day-to-day.
Practical: Most men feel steadiest on enanthate weekly or every 10 days. This is the preferred injectable form for most.
Cost: NHS Sustanon is usually free. Private enanthate costs £25–50/month.
Testosterone Undecanoate (Nebido)
What it is: A long-acting ester with a 20+ day half-life. One injection lasts approximately 10–14 weeks.
UK availability: Available on NHS and private prescription, though less common than Sustanon.
Mechanism: Absorbed from intramuscular depot, providing steady release for months.
Dose: 1000 mg per injection.
Injection frequency: Once every 10–14 weeks. Very convenient.
Downsides:
- Less fine-tunable: If you get side effects or your dose is too high, you're stuck with it for months (can't easily dial back)
- Larger volume: Single injection is 4 ml (intramuscular, usually in buttock)
- Peak/trough: Despite long duration, there's still peak at 2–4 weeks and trough approaching the next injection. Some men feel noticeably different between weeks 6–10 of the cycle
- Cost: Expensive (£300–400 per 10-week supply in UK)
Practical: Excellent for convenience if you're on a stable dose and tolerating it well. Not ideal for initial titration or if you're likely to need dose adjustments.
Injection Sites
Intramuscular (IM) Injections
Traditional injection into muscle. Common sites:
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Buttocks (Glute max): Most common. Needle 1–1.5 inches, 25G needle. Inject in upper outer quadrant (avoid lower medial area where the sciatic nerve is).
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Thigh (Vastus lateralis): Outer thigh, midway between hip and knee. Needle 1–1.25 inches, 25G needle. Usually less painful than glute.
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Shoulder (Deltoid): Needle 0.625–1 inch, 25G needle. Smaller muscle, so typically only for volumes < 1 ml.
Advantages: Can handle larger volumes (up to 2–3 ml per injection).
Disadvantages: Deeper injection, slightly higher infection risk if technique is poor, can be painful.
Subcutaneous (Sub-Q) Injections
Injection into the fat layer beneath the skin (not into muscle). Common sites:
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Abdomen: Grab the skin layer, pinch, inject shallow (0.5 inch needle, 27–29G needle) at 45-degree angle into the fat.
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Upper thigh: Similar technique.
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Side of chest: Possible but less common.
Advantages:
- Less painful (smaller needle, shallower injection)
- Lower infection risk (easier to maintain sterility with shallow injection)
- Easier to self-inject (don't need to reach your buttock)
- Increasingly evidence suggests equally effective and potentially more stable levels than IM
Disadvantages:
- Limited to lower volumes (typically < 1 ml per injection). If your dose requires > 1 ml, you need IM
- Older guidance suggested sub-Q was inferior to IM, but recent evidence doesn't support this
Modern practice: Sub-Q is increasingly preferred for home injection because it's easier, less painful, and equally effective.
Needle Sizes and Gauges
Gauge: Higher number = thinner needle.
- 25G: Standard for IM. 0.5 mm diameter. Good balance of easy insertion and less tissue trauma.
- 27G: Standard for sub-Q. Smaller, less painful, used for shallower injection.
- 29G: Very small, used for sub-Q if you want minimal pain.
Length:
- IM buttock: 1–1.5 inches (depending on body fat)
- IM thigh: 1–1.25 inches
- IM deltoid: 0.625–1 inch
- Sub-Q: 0.5–0.625 inches
Practical: Start with 25G 1-inch for IM (standard), or 27G 0.5-inch for sub-Q (if < 1 ml per injection).
Injection Technique: How to Inject
Basic Safe Injection Protocol
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Wash hands thoroughly with soap and water.
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Prepare equipment:
- Vial of testosterone
- Alcohol swab
- Syringe (appropriate size for your dose — typically 1 ml or 3 ml syringe)
- Needle (one for drawing, ideally a different one for injecting — reduces blunting)
- Sterile gauze
- Sharps bin for safe disposal
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Draw the testosterone:
- Wipe the rubber stopper of the vial with an alcohol swab
- Draw air into the syringe equal to the volume you're withdrawing
- Insert needle into vial (bevel down), inject the air
- Invert vial, draw the testosterone into the syringe
- Tap the syringe to remove air bubbles
- Withdraw needle from vial
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Prepare injection site:
- Choose your site (alternating between sides if using gluteal or thigh injections)
- Wipe with an alcohol swab, let it dry completely (alcohol prevents proper sealing and is painful if injected)
- For IM: locate your injection site (upper outer gluteal quadrant, or outer thigh midpoint)
- For sub-Q: pinch a fold of skin
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Inject:
- Ensure you're using a fresh needle for injection (change from drawing needle if possible)
- For IM: Insert needle at 90-degree angle with one smooth motion. Aspirate (pull back on plunger) to check you haven't hit a blood vessel. Inject slowly over 3–5 seconds.
- For sub-Q: Insert at 45–90 degree angle into the pinched skin fold. No need to aspirate. Inject slowly.
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Withdraw:
- Remove needle smoothly
- Apply pressure with sterile gauze for 10 seconds
- No need for a plaster unless there's bleeding
Common Mistakes to Avoid
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Reusing needles: Dulls the needle, increases pain, increases infection risk. Use a fresh needle for injection even if you drew from the same syringe.
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Injecting while alcohol is wet: Painful and can prevent proper sealing. Let the alcohol dry completely (10–15 seconds).
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Injecting too fast: Causes pain and inflammation. Inject over 3–5 seconds.
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Not using aseptic technique: Wash hands, use fresh swabs, don't touch the needle tip after it's been opened.
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Hitting a blood vessel (IM): Rare, but aspirating prevents this. If you aspirate and get blood, withdraw the needle and try a slightly different site.
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Injection site reactions: Usually from injecting when alcohol is still wet, dirty technique, or reused/dulled needles. Proper technique prevents this.
How Often to Inject
This depends on your testosterone ester:
Sustanon 250
250 mg weekly (most common) or 250 mg every 5–7 days (if you want more consistent levels).
Testosterone Enanthate or Cypionate
- Weekly: 100–200 mg every 7 days (most common)
- Every 10 days: 150 mg every 10 days
- Every 14 days: 200 mg every 14 days (less ideal — more peak/trough)
Most men feel best with enanthate 100–200 mg weekly.
Testosterone Undecanoate (Nebido)
1000 mg every 10–14 weeks.
Practical: Peak-Trough Concept and Why Frequency Matters
Testosterone levels rise after injection and then decline until the next injection. This peak-trough cycle affects how you feel.
Example: Enanthate 200 mg weekly
- Day 1 (post-injection): 200 ng/dL
- Day 3 (peak): 700 ng/dL
- Day 7 (pre-injection): 450 ng/dL
A 250 ng/dL fluctuation throughout the week. Some men feel great at the peak, terrible at the trough.
How to minimise peak-trough:
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More frequent, lower-dose injections: Instead of 200 mg weekly, do 100 mg every 3.5 days. This produces smaller peaks and shallower troughs, more stable overall levels.
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Longer-duration ester: Sustanon or enanthate every 14 days instead of weekly (but this worsens peak-trough). Undecanoate every 10 weeks has minimal peak-trough.
Practical: If you notice mood/energy swings throughout your injection cycle, switching to more frequent injections (e.g., twice weekly instead of once weekly) often improves this dramatically.
Tracking Your Response
Keep a simple log:
- Injection date, time, amount, site
- How you feel that day and the next 2–3 days: Energy, libido, mood, gym performance
- Any side effects: Acne, injection site pain, anything unusual
- Monthly summary: Overall sense of energy, libido, mood, body composition changes
This helps identify patterns. Example: you notice you feel best on day 2–4 after injection, and your mood is flat by day 6–7. This tells you your frequency might not be optimal.
Safe Disposal
Needles and syringes must be disposed of in a sharps bin (a specially designed rigid plastic container).
Obtaining a sharps bin:
- Your GP can provide one for free
- Private TRT clinics provide them
- Pharmacies sell them (£5–10)
Never dispose of needles in regular waste. Once your sharps bin is full, you can return it to a pharmacy or GP for safe incineration.
Common Questions
Does testosterone injection hurt?
Properly done, subcutaneous injection is usually painless or minimal discomfort. Intramuscular can be slightly more uncomfortable, but it's brief. Most pain comes from improper technique (blunt needle, wet alcohol, injecting too fast).
Can I inject myself?
Yes. Most men self-inject either subcutaneously (easier) or intramuscularly (slightly more difficult but manageable). You may want a GP, nurse, or partner to demonstrate the first time.
Can I use a smaller needle to reduce pain?
For sub-Q, yes — smaller gauge (29G) reduces pain. For IM with large volumes (> 2 ml), you need a larger needle. For standard 1–1.5 ml volumes, 25G is fine.
What if I miss an injection or inject late?
Once weekly: if you're 1–2 days late, it's fine — just inject the next dose. If you're several days late, you'll probably feel it (lower testosterone), but one missed week isn't catastrophic. Resume your schedule.
Can I change injection sites?
Yes, and you should rotate. Injecting the same site repeatedly can cause scar tissue, cysts, or chronic irritation. Alternate between left and right glute (or thigh), or use sub-Q abdomen on alternating sides.
Should I split the dose?
If your weekly dose is < 1.5 ml and you're using sub-Q, one injection is fine. If > 2 ml or you prefer more stable levels, splitting into two injections per week (half dose each) is reasonable.
Working With Your Doctor
If you're prescribed testosterone injections, your doctor (or TRT clinic) should:
- Teach you proper injection technique (in person ideally, or via video)
- Prescribe appropriate needles and syringes
- Provide sharps bin for safe disposal
- Monitor testosterone levels (blood tests at 4–6 weeks, then periodically)
- Monitor side effects (haematocrit, lipids, liver function, prostate PSA)
- Adjust dose based on your response (how you feel + blood results)
If your doctor doesn't do these things, find a different clinic. Testosterone injection is straightforward, but it requires proper oversight.
The Bottom Line
Testosterone injection is practical, cost-effective, and for most men, the preferred form of TRT. Subcutaneous injection is becoming the standard for home injection — it's less painful, easier, and equally effective.
Proper technique is important: clean hands, clean skin, fresh needle, inject slowly, rotate sites, dispose safely.
Most men become comfortable with self-injection within 2–3 attempts. Once you've got the technique down, injecting takes 2–3 minutes weekly (or every 10 days, depending on your protocol).
The key is consistency: same dose, same frequency, proper monitoring. Done right, injectable TRT is reliable, predictable, and well-tolerated.