The most common self-diagnosis we hear from men with erection problems: "my testosterone must be low." It's an understandable guess — testosterone is the male hormone, erections are a male function, and the internet connects the two daily. It's also usually wrong. Most erectile dysfunction is not a testosterone problem, and taking testosterone won't fix it.
But sometimes the guess is right — and there's a specific pattern that tells you when. This article covers what testosterone actually does for erections, when the two problems connect, the blood tests that settle it, and why treating the wrong one wastes months.
What testosterone actually does for erections — and what it doesn't
Testosterone's main sexual job is upstream: desire. It drives sexual thoughts and interest, supports arousal responsiveness, and contributes to the frequency of spontaneous night-time and morning erections. It also underpins energy and mood — the platform sex sits on.
What testosterone doesn't do is operate the machinery. An erection is a neurovascular event: arousal fires a nerve signal, the signal releases nitric oxide in the penis, smooth muscle relaxes, blood flows in and stays in. That plumbing runs on nerves and blood vessels, not on hormone levels — which is why men with genuinely low testosterone can often still get erections, and men with excellent testosterone can have severe ED.
The caricature that's clinically useful:
- Low testosterone sounds like: "I could, but I don't really want to. I barely think about it any more."
- Vascular ED sounds like: "I want to, but it won't cooperate."
Real men are messier than caricatures — but the desire-versus-mechanics split is the single most useful question in sorting this out.
Most ED is not low testosterone
BPAC, the NZ primary-care guidance body, is blunt about it: "most males with erectile dysfunction do not have low testosterone levels." Its guidance goes further — testosterone testing is usually unnecessary when ED is the only symptom, with no other features of hormone deficiency.
What actually dominates ED, per Healthify's breakdown of causes: vascular disease (narrowed vessels, driven by diabetes, high blood pressure, high cholesterol and smoking), nerve damage, medication side effects (antidepressants and some blood-pressure medicines are common culprits), and psychological causes (stress, depression, performance anxiety, relationship strain). Hormonal causes are on the list — low testosterone, thyroid disease, high prolactin — but they're the minority share.
This matters because ED with normal testosterone is often a vascular early warning: Healthify notes erection problems can be an early sign of diabetes and heart disease. Chasing a hormone that was never the problem is how that warning gets missed.
When to suspect the hormonal version
Not from one symptom — from the cluster. The pattern BPAC identifies as most indicative of testosterone deficiency is the sexual trio occurring together:
- Low sexual desire — fewer sexual thoughts, not just less sex
- Erectile dysfunction
- Fewer morning erections
Around that trio sit the non-specific symptoms: fatigue and falling motivation, low mood, sleep disturbance, creeping body-composition change (less muscle, more middle). Each is meaningless alone — every tired 45-year-old has half of them. Together with the sexual trio, they start to mean something.
Context raises the odds too: BPAC lists obesity, type 2 diabetes and insulin resistance among the factors associated with low testosterone — the same metabolic ground that produces vascular ED, which is why the two problems can and do coexist.
If you want a structured way to organise your symptoms before bloods, the AMS questionnaire is the standard screening tool — a symptom score, not a diagnosis. For the fuller picture of the deficiency syndrome, see signs you might need TRT.
The bloods that settle it
One blood test doesn't diagnose anything here. The standard, per BPAC guidance:
- At least two morning total testosterone measurements — drawn between 7 and 11 am, ideally fasted, because testosterone peaks in the morning and falls through the day
- Taken on separate days, typically about four weeks apart — levels swing with illness, poor sleep and lab variation, and a treatment decision shouldn't hang on one reading
- Interpreted with SHBG and calculated free testosterone in borderline cases
- Followed by LH, FSH and prolactin if low — these locate the problem: raised LH points to the testes (primary), low or inappropriately normal LH points to the pituitary or hypothalamus (secondary), and prolactin catches a specific, treatable cause that's easy to miss
There's no single magic number: thresholds differ between guidelines, so symptoms and repeated morning levels are read together. An afternoon reading taken once, during a rough week, settles nothing — and starting long-term hormone therapy on the strength of one is how men end up treated for a condition they never had.
What happens when both coexist
Some men genuinely have both: confirmed low testosterone and erectile dysfunction. Most often it's middle-aged men with the metabolic pattern — weight, insulin resistance, blood pressure — that erodes both hormone production and blood-vessel function at the same time.
The treatment logic, honestly stated:
- Confirmed deficiency gets treated. In NZ, the injectable depot testosterone products are fully funded — no Special Authority required — where hypogonadism is confirmed. What restoration mainly delivers is desire, energy and mood.
- The erectile mechanics often still need their own treatment. BPAC's assessment is that testosterone alone is not an effective strategy for moderate-to-severe ED, and that adding testosterone to a PDE5 inhibitor probably adds little for erections beyond what the PDE5 inhibitor does. Desire is hormonal; plumbing is vascular. Each gets its own tool.
- The funding is asymmetric. Testosterone for confirmed deficiency: funded. PDE5 inhibitors for general ED: not funded in NZ — a private script, whoever prescribes it.
- The shared drivers get treated too. BPAC's first-line move is the modifiable factors — weight, physical activity, smoking, co-morbidities. It's the only intervention that improves both problems at once.
Why treating the wrong one fails
Testosterone for a normal-testosterone man with ED: desire may nudge, the mechanics don't move — that's BPAC's monotherapy point — and you've taken on real costs for nothing. External testosterone suppresses your own production and fertility while you're on it, commits you to ongoing monitoring (haemoglobin and haematocrit among it), and, worst, leaves the actual cause unexamined. If that cause was vascular, it's still progressing.
A PDE5 inhibitor for a hormonal problem: the tablet improves blood flow, so the erections work when you try — but desire stays absent, so you stop trying, conclude "treatment doesn't work", and the deficiency (and whatever's driving it, including the pituitary causes) goes unexplored.
Either drug for a psychological problem: treats the wrong organ entirely.
None of this is an argument against treatment. It's an argument for sequence: diagnosis, then treatment. The fix costs a couple of early-morning blood draws. The alternative costs months on the wrong path.
How we approach it at Enhanced Men
Both doors lead to the same discipline. Whether you come in through the ED treatment NZ service or the TRT service — testosterone replacement therapy in NZ, the first step is identical: a history that separates desire from mechanics, cardiovascular and metabolic risk, medication review, and morning bloods — testosterone included when the pattern justifies it. The initial consult is $149 either way — telehealth, NZ-wide, no referral needed.
Then we treat what the results actually show. ED with normal testosterone gets ED treatment and a straight answer about why testosterone isn't it. Confirmed deficiency gets the TRT pathway with proper monitoring. Both together get both — with honest expectations about which treatment does which job.
FAQ
Will taking testosterone fix my ED? Usually not. Most men with ED have normal testosterone, and BPAC's guidance is that testosterone alone is not effective for moderate-to-severe ED even when levels are low. It treats desire, energy and the deficiency syndrome — the erectile mechanics usually need their own treatment.
Can my testosterone be normal and my ED still be real? Yes — that's the most common situation. ED with normal testosterone is typically vascular, neurological, psychological or medication-related, and it deserves a workup on those fronts — especially a cardiovascular and metabolic check.
What testosterone level causes ED? There's no single cut-off. Diagnosis rests on at least two morning total testosterone readings below the reference range, on separate days, interpreted alongside symptoms. Thresholds vary between guidelines, which is why one number in isolation proves little.
Is testosterone treatment funded in NZ if my ED turns out to be low testosterone? If hypogonadism is confirmed, the injectable depot testosterone products are fully funded in NZ — there is no Special Authority to apply for. The ED tablets are the opposite: no PDE5 inhibitor is funded for general erectile dysfunction in NZ, so that side stays a private prescription.
Should I do a questionnaire before getting bloods? The AMS questionnaire is a reasonable structured starting point — it organises your symptoms and gives you something concrete to bring to a consult. It can't diagnose anything. Two morning blood tests can.
References (NZ-specific)
- BPAC NZ — Prescribing testosterone in ageing males (2024): https://bpac.org.nz/2024/testosterone.aspx
- Healthify NZ — Erectile dysfunction: https://healthify.nz/health-a-z/e/erectile-dysfunction/
- Healthify NZ — Sildenafil for erection problems: https://healthify.nz/medicines-a-z/s/sildenafil-for-erection-problems
This article is general health information, not personalised medical advice. Both erectile dysfunction and testosterone deficiency need proper clinical assessment and blood testing — self-diagnosis in either direction is how men end up on the wrong treatment.