Switching TRT Formulations in NZ: A Doctor's Guide

If you're already on testosterone replacement therapy and reading this, there's a reasonable chance you're not entirely happy with your current protocol. Maybe the gel rubbed off and you never quite trusted it. Maybe your three-weekly Sustanon shot has you feeling great for ten days and flat by day eighteen. Maybe you're on Reandron and the four-month cycle means a brilliant first month and a grim last one. Maybe you're sick of driving to the practice for an injection you could give yourself in two minutes.

Switching between testosterone formulations is one of the most common reasons men come to Enhanced Men. The good news: every funded testosterone in NZ can be switched to every other funded testosterone, the switch itself is usually straightforward, and you don't need to come off therapy to do it. The reasons it's not as simple as "just change the script" are timing, bloodwork, and getting the new dose right — and that's what this article walks through.

The four funded options, recapped

All four deliver the same molecule — testosterone — into the same receptors. What differs is the release curve, the dosing interval, and the practicality of self-administration. Switching is essentially a curve-shape change at a similar total weekly dose. The cypionate and Sustanon depot guide breaks down each formulation in more depth.

Why people switch

In our practice the most common switches, and the reason men ask for them:

• Gel → injectable. Daily application fatigue, transfer-to-partner concern, inconsistent absorption, prefer the simplicity of one weekly injection.
• Sustanon (3-weekly) → cypionate (weekly or fortnightly). Wanting a flatter curve. The classic "great in week one, flat by week three" cycle is exactly what splitting the dose fixes.
• Reandron (10–14 weekly) → cypionate or Sustanon. Reandron's long interval is convenient on paper, but the trough months feel real for some men. Shorter intervals give finer control.
• Clinic-administered → self-administered. Same drug, same dose, different logistics. Removing the practice-visit step changes adherence dramatically.
• Injectable → gel. Less common but legitimate — needle aversion, planned fertility window where a faster-clearing option helps, or BPAC-first-line gel never having been properly trialled.

If your reason for wanting to switch isn't on this list, it's still a valid conversation. There's no clinical hierarchy — what matters is which protocol fits your life and gives you the steadiest bloodwork.

How the switch is actually done

A switch is not a "stop and restart." Stopping testosterone abruptly and waiting before starting again would just give you a few weeks of low testosterone for no reason. The switch is a timing problem: you start the new formulation as the old one is releasing its last dose, so your serum level stays in range through the transition.

Gel → injectable

The most common direction. Gel half-life is hours, so your levels are essentially dependent on yesterday's application.

• Last day of gel: the day before your first injection.
• First injection: the next morning.
• Re-check bloods: trough at 6–8 weeks.

The handover is almost seamless. Most men describe a small "settling" period of 2–3 weeks while their body adapts to the new curve shape, then steady-state.

Sustanon (3-weekly) → cypionate (weekly or fortnightly)

This is one of the most-requested switches.

• Last Sustanon injection as scheduled.
• First cypionate injection at week 2 after the Sustanon shot — when the decanoate ester is starting to fall but still contributing. Starting earlier risks a small overshoot; starting later risks a dip.
• Dose: roughly the same total weekly equivalent. If you were on 250 mg Sustanon every 3 weeks (≈ 83 mg/week), a starting cypionate dose around 80–100 mg weekly lands in the same range.
• Re-check bloods: trough at 6–8 weeks on the new protocol.

Most men feel the difference within 4–6 weeks — flatter mood, libido and energy across the week, less of the cycle they'd grown used to.

Reandron → cypionate or Sustanon

Reandron has a long tail. Switching too early gives you the new drug's release stacked on top of Reandron still leaving.

• Last Reandron injection as scheduled.
• First cypionate (or Sustanon) injection at around week 10–12 after the Reandron shot — the point at which trough levels are starting to fall but you haven't dropped out of range. Some protocols wait the full 14 weeks; we tend to start at 10–12 to avoid a pronounced dip.
• Dose: total weekly equivalent of where Reandron was holding you. If your trough on Reandron was sitting around 12–14 nmol/L, start somewhere around 80–120 mg cypionate weekly and let bloods guide.
• Re-check bloods: trough at 8 weeks (longer than the other switches because some Reandron is still clearing).

Allow 3 months for the new pattern to feel like a steady state. The first month of any new injectable protocol after Reandron can be the most variable — that's the long-ester decay overlapping with new-drug onset.

Injectable → gel

Less common but a clean switch.

• Last injection as scheduled.
• Start gel at the point your trough would normally fall. For weekly cypionate: 5–6 days after the last shot. For Sustanon: around week 2 post-injection.
• Dose: standard funded gel dose (usually 40.5 mg daily, two sachet pumps).
• Re-check bloods: trough at 6 weeks — but on gel, the timing of the blood draw relative to the morning application matters. Standardise to "before today's gel" for consistency.

Bloodwork at the switch

Two timepoints matter:

• Pre-switch baseline (optional but useful). A trough drawn just before the last dose of the old formulation. This tells you what level the old protocol was actually delivering you, which makes the new dose easier to land.
• Post-switch trough at 6–8 weeks (8 weeks for the Reandron switch). The new formulation will have reached steady state by then. This is the dose-decision blood.

Both timepoints can be done at your local lab on a private request form. A focused panel at the switch point usually includes: total + free testosterone, SHBG, oestradiol, haematocrit (FBC), and a check of lipids and HbA1c at the same draw if it's been a while.

The single number to watch through every switch is haematocrit — see the polycythaemia article for thresholds and the venesection pathway if it climbs.

What to expect in the transition window

A few things that are normal and aren't a sign the switch went wrong:

• 2–3 weeks of subjective unsettledness. Mood, sleep and libido can shift while your body adapts to the new curve. This isn't the new drug "not working" — it's the receptor system adjusting to a different release pattern.
• A small change in side-effect profile. Acne, oestradiol-related symptoms (mood, water retention), or sleep can transiently shift. Sometimes for the better, sometimes for the worse. Usually back to baseline by week 6.
• A different injection-day pattern if you were on Sustanon. The week-one peak you used to feel with Sustanon flattens out on weekly cypionate. Some men miss it; most don't.
• Slower onset feels-better window if switching from injectable to gel. Gel takes 2–3 weeks to reach steady state from a standing start.

If the 6–8 week trough sits well outside target, the dose is adjusted — not the formulation switched back. Most "the new drug isn't working for me" stories are actually dose-titration stories that hadn't been given enough time.

What we do at Enhanced Men

Most switches we manage are Sustanon → weekly cypionate or gel → weekly cypionate, both subcutaneously self-injected at home. We handle the timing, the lab request, the dose calculation, and the 6–8 week review with bloodwork interpretation. If you want to stay on Sustanon or Reandron and just fine-tune the protocol, we'll happily do that — there's no formulation we won't manage.

What we don't do is push everyone toward the same script. The right answer for a 38-year-old who self-injects at home and the right answer for a 62-year-old who'd rather drive to a clinic every three weeks are different answers.

FAQ

Can I switch without stopping TRT? Yes — and you should. The whole point of switching (rather than restarting) is keeping your level in range through the transition. Stopping for weeks before starting the new drug just gives you a stretch of low testosterone for no reason.

Will my Pharmac funding follow me to the new formulation? Yes. All four funded formulations are on the standard Pharmac TRT pathway. The script changes; the funding doesn't.

Do I need to see a specialist to switch? No. Any GP or registered medical practitioner with the appropriate experience can manage a switch. If your current prescriber is comfortable, they can do it. If you want a fresh set of eyes or are running into "we only do Sustanon here," that's where we come in.

How long until I feel "settled" on the new one? 6–8 weeks for most men. Up to 3 months after coming off Reandron because of the long ester tail.

Do I have to start self-injecting just because I'm switching to cypionate? No. Cypionate can be clinic-administered every 2–3 weeks if that suits you better — same drug, same script, different injection setting. Self-injection is an option we teach when patients want it, not a requirement.

What about going off TRT entirely? That's a different conversation. If you're considering coming off TRT (not switching, stopping), the coming off cycle guide covers the HPG-axis recovery pathway — the same principles apply to therapeutic TRT.

I'm on TRT through a different NZ clinic — can you take over? Yes. A clean handover involves a copy of your current script, your most recent bloods, and one consult to confirm protocol and bloodwork plan. No coming off, no gap.

References (NZ-specific)

• BPAC NZ — Prescribing testosterone in ageing males (2024)
• New Zealand Formulary — testosterone esters monographs (nzf.org.nz)
• Pharmac — Pharmac to fully fund testosterone gel for all who need it (Feb 2024)
• Medsafe NZ — Depo-Testosterone data sheet
• Medsafe NZ — Sustanon data sheet
• Medsafe NZ — Reandron data sheet
• Endocrine Society — Testosterone Therapy in Men with Hypogonadism: Clinical Practice Guideline

This article is general health information and does not replace personalised medical advice. Switching TRT formulations is a clinical decision that depends on your current regimen, bloodwork, symptoms and goals — work it through with a doctor who can see the full picture.