ED Isn't Only About Blood Flow

If you've been asking yourself why do I have ED, the real answer is that it could be several things at once, most of them findable and most of them treatable. One of them is worth knowing about years early.

Below: how an erection works, the four cause categories, why the famous pill sometimes misses, and what to do about it.

What causes ED besides blood flow?

Erectile dysfunction can start in any of four systems: the brain that initiates arousal, the nerves that carry the signal, the blood vessels that execute it, and the hormones that set the baseline. Vascular trouble is the most common cause, most cases involve more than one system, and all four categories are treatable.

The Old Story: ED as a Plumbing Problem (and Why It's Incomplete)

Medicine has told two stories about what's behind ED, and both were too simple. For most of the last century, the assumption was that ED lived in your head. Johns Hopkins' patient guide notes the field now knows the opposite is closer to the truth: for most men the problem is physical, usually starting with the blood supply. The correction overshot into the plumbing-only story that dominates the category today, where every funnel ends at the same pill.

So what causes erectile dysfunction besides blood flow? The nerves that carry the signal, the hormones that set the baseline, and the brain that generates arousal in the first place. Mayo Clinic puts arousal's ingredient list six deep:

• brain

• hormones

• emotions

• nerves

• muscles

• blood vessels

A problem with any one can cause ED, and per UCSF they frequently come in combination.

How an Erection Actually Works: Four Systems, Not One

An erection is a coordinated event: the brain initiates, the nerves carry, the blood vessels execute, and hormones set the baseline. The chain, in order:

1. The brain starts it. Arousal is a neurological event first. Dopamine signaling deep in the brain, the central arousal pathway, fires the opening request.
2. The nerves carry it. The request runs down the spinal cord to the pelvic nerves, whose endings release nitric oxide (NO) in the penis.
3. The vessels execute. Nitric oxide raises a messenger called cGMP, smooth muscle relaxes, and the corpora cavernosa, two sponge-like cylinders, flood with blood.
4. Hormones set the baseline. Testosterone, governed by the hypothalamic-pituitary-gonadal (HPG) axis, keeps desire alive and the tissue responsive. It's the thermostat, not the trigger.

Clinicians sort ED by where the chain breaks. Cleveland Clinic names four types, vascular, neurogenic, hormonal, and psychogenic ED, and plenty of men sit in more than one column.

The chain also explains the pills. PDE5 inhibitors act on step three only, protecting cGMP so the vascular response runs stronger, and the FDA label is blunt that without sexual stimulation they do nothing. They amplify a signal; they can't create one. Keep that in your pocket, it's half the answer to why they don't work for everyone.

Vascular: Blood Flow Is Real (and Often the First Domino)

Vascular trouble is the most common type of ED, and it's the one the famous pills were built for. Cleveland Clinic ranks vascular ED as the most common type, and Johns Hopkins agrees that blood vessel problems lead the cause list. The mechanism is unglamorous: the arteries feeding the penis are smaller than the ones feeding your heart, and everything that stiffens or clogs arteries, high blood pressure, high cholesterol, smoking, extra weight, reaches them early.

Declining endothelial function, the vessel lining's ability to relax and open on demand, tends to show up here first. Trouble maintaining an erection, losing it too quickly, is often the early vascular sign, and atherosclerosis is the classic reason. Hold that thought; it comes back when we get to your heart.

Diabetes earns its place in this column twice, damaging vessels and nerves at once, with metabolic syndrome and insulin resistance sitting right beside it on Mayo's cause list; Hopkins puts ED prevalence in men with diabetes at 35 to 50 percent.

This is the pathway a PDE5 inhibitor (tadalafil, sildenafil) serves, and on home turf the class is excellent. In the fixed-dose trials on the FDA label, 63, 74, and 82 percent of men taking sildenafil at 25, 50, and 100 mg reported improved erections, against 24 percent on placebo.

Tadalafil's label brings range: improved erectile function versus placebo up to 36 hours after dosing, absorption unaffected by food, and a once-daily option that takes scheduling off the table.

If your pattern reads vascular, tadalafil and sildenafil are available through algorx as FDA-approved generics, with pricing visible before checkout. An independent licensed provider reviews your health questionnaire, typically within 24 to 48 hours, and prescribes only where appropriate; eligibility and state availability apply, and approval is never guaranteed. One hard rule: if you take nitrates in any form, these medications are off the table, because the combination can drop blood pressure to dangerous levels.

Neurological: The Brain-to-Body Signal

Neurogenic ED means the message can't get through: the vessels may be perfectly capable, but the request never arrives. Cleveland Clinic's definition is exactly that, nerve problems keeping signals from traveling from brain to penis. The neurological causes of erectile dysfunction worth knowing:

• Multiple sclerosis and other nerve disorders

• Spinal cord injuries and nerve damage

• Pelvic surgery, prostate procedures especially, and radiation to the area

• Stroke

• Diabetic neuropathy, nerve damage from years of high blood sugar

If your ED started after an injury, an operation, or a new diagnosis on this list, that timing is diagnostic gold; say it early in any evaluation. This category is also the clearest case for why the guidelines make a real history and exam part of any proper evaluation: the right fix depends on what broke.

Hormonal: Testosterone, Prolactin, Thyroid, and the Desire-vs-Mechanics Gap

Can low testosterone cause ED? It can contribute, but it's rarely the whole story, and it's one of the few causes a blood test can catch. Johns Hopkins' guide is blunt: low testosterone is rarely the sole factor behind ED. The numbers agree. In one series of 1,022 men evaluated for ED, repeatedly low testosterone turned up in 4 percent of men under 50 and 9 percent of men 50 and older.

The hormonal causes of ED cluster around three hormones:

• Testosterone sets the baseline: desire, responsiveness, some of the vascular tone. The catch with erectile dysfunction and testosterone is that the link runs mostly through desire, and the trials showing treatment modestly improve libido and erectile function enrolled men with confirmed deficiency.

• Prolactin, when elevated (hyperprolactinemia), suppresses the signals that drive testosterone production. It shows up in about 2 percent of workups, but it's findable, and marked elevations are treatable once a provider finds the cause.

• Thyroid dysfunction in either direction tracks with ED: in one study of 71 men with thyroid disease, 79 percent scored in the ED range against 34 percent of controls, and scores improved after treatment. A TSH test is how you look.

This is where the low libido vs erectile dysfunction distinction earns its keep. Pills address mechanics; if the real problem is wanting, a hormone panel beats a bigger dose.

The anchor test is a morning total testosterone. The AUA guideline is specific about it: every man with ED should have his total testosterone measured on a morning draw, and the diagnostic standard is two early-morning draws on separate occasions, never one reading. Ask for SHBG and free testosterone alongside the total, especially if you carry extra weight or have diabetes: both lower SHBG, making total read low while free testosterone can still sit normal.

If two proper draws confirm a deficiency, testosterone replacement is one route, though algorx does not offer TRT or prescribe testosterone. For the man with a confirmed deficiency who'd rather ask his own axis for more, we've written a full guide to treating low testosterone and what an independent provider weighs before agreeing to it.

Psychological: Anxiety, Stress, and the Performance Loop

Can ED be psychological? Yes, and more often than most men expect: UCSF's clinicians hold that psychology plays at least some part in virtually every case. Pure psychological erectile dysfunction, where the machinery is fine and the mind carries the whole story, is the minority; the mix is the norm.

The tightest link is between ED and anxiety, and it works as a loop. One bad night, from stress, alcohol, exhaustion, or nothing you can name, plants a worry; next time, part of your attention is scanning for failure, the opposite of the state the chain runs on. Cleveland Clinic's therapists call it a vicious cycle and estimate performance anxiety touches up to a quarter of men.

Depression runs both directions here: depressed men carry higher odds of ED, and men with ED carry almost three times the odds of developing depression, which is why the AUA tells clinicians to consider a mental-health referral as part of ED care.

So is your ED physical or mental? The honest markers, and their limits: if it works sometimes and not others, that situational erectile dysfunction pattern points psychological. So do intact morning erections; clinicians read nocturnal erections as evidence the hardware works, though the guideline's careful wording is that this suggests, and does not confirm, a psychogenic component. Intact mornings don't rule out an underlying condition, and the physical vs psychological ED question is one an evaluation settles better than a hunch.

If the psychological side of this is loud, treat it as seriously as any lab number. Therapy and sex-specific counseling help even when the cause is partly physical, and they belong to the standard of care, not the consolation prize.

ED in Your 20s and 30s: Why Young Men Get It

Why do young men get ED? The same four systems, with the odds shifted toward the psychological, and it's far more common than the stereotype allows. In a study of consecutive men arriving at a sexual-medicine clinic with new ED, one in four was under 40. Two numbers from that study belong side by side:

• 90 percent of those under-40 patients had no other medical conditions on record.

• Severe ED was more common among them than among the older men.

Read together: the causes of erectile dysfunction in young men are usually not a failing body, and the problem still deserves the same straight-faced evaluation at 28 that it gets at 58.

Field reviewers note that most ED in younger men likely has a psychogenic basis, and a Mayo urologist puts it plainly: when young men struggle, most of the time it's a confidence issue. Confidence responds to treatment, sometimes medication to break the loop, sometimes a therapist trained in exactly this, often both.

What counts as a problem worth evaluating? A consistent difficulty lasting more than three months; the occasional bad night is normal at every age. And there's one more reason not to shrug it off young: in your 20s, 30s and 40s, ED is at its most informative, which is where we're headed next.

Why ED Can Be an Early Warning Sign for Your Heart

Is ED a sign of heart disease? It can be, and the urology guideline says so plainly: it tells clinicians to counsel men with ED that the condition signals raised risk of underlying cardiovascular disease. The link between erectile dysfunction and cardiovascular disease is unusually well documented.

The reason is the vascular story run forward in time. The penile arteries are smaller than the coronary arteries, so when the vessel lining starts failing, erections often falter before the chest complains. Johns Hopkins' cardiology reviewers describe endothelial dysfunction as one of the first stages of coronary heart disease, and one that often shows in the penis first.

In one study of 300 men with established coronary disease, erectile trouble had arrived first for roughly two out of three, on average about three years ahead, and the AUA's summary is that ED can precede a cardiovascular event by up to five years. A Mayo urologist goes further: especially in younger men, erections can flag a heart attack or stroke years before it announces itself.

The numbers: in a population study that followed men for a decade, men in their 40s with ED developed coronary disease at 48.5 per 1,000 person-years, against roughly 1 per 1,000 for their ED-free peers, and the authors' conclusion was that young men with ED may be ideal candidates for cardiovascular screening.

Among more than 1,900 men aged 60 to 78, those reporting ED had about twice the rate of heart attacks, cardiac arrests and strokes over four years, after adjusting for the usual risk factors. And in trial data cited by the AUA, ED predicted future cardiac events about as strongly as smoking or a family history of heart attack.

None of this makes ED a diagnosis. It makes ED information that arrives early enough to use:

• Tell your PCP the whole picture, ED included; it changes what gets checked.

• Get the basics measured: blood pressure, lipids, glucose or A1c.

• Treat what turns up. In one two-year trial, about a third of obese men got normal erectile function back on a structured diet-and-exercise program, no pills involved.

Why the Blue Pill Doesn't Work for Everyone (Central vs. Peripheral)

"Why don't ED pills work for me?"

For a real share of men the honest answer is that the pill hasn't failed yet, because it was never given a fair shot. Up to 30 to 40 percent of men get little or no response from their first course of an on-demand PDE5 inhibitor. What studies of PDE5i non-responders found behind that number is a genuinely fixable list:

• Wrong use, more than half the time. In one clinic's run of 100 consecutive non-responders, 56 were taking the pill incorrectly: 45 had never tried the full dose, 32 took it right after a meal, 22 took it moments before sex, and 12 didn't know sexual stimulation was required.

• No follow-up. With re-instruction and dose adjustment, roughly a third to half of "non-responders" respond after all, and the fix holds; in one series, 94 percent were still responding two years later. Switching to once-daily tadalafil, an FDA-approved regimen, rescued 58 percent of on-demand non-responders. Instructions and titration are AUA standard of care for a reason.

• An untreated cause underneath. A confirmed testosterone deficiency the pill can't compensate for. Advanced vascular disease, diabetes especially. Nerve injury after prostate surgery or radiation, the genuinely hard case. And some everyday prescriptions, certain antidepressants and blood pressure medications among them, can work against erections; that's a conversation with your prescriber, never a reason to stop anything on your own.

Then there's the group the vascular pill was never aimed at. PDE5 inhibitors work on the peripheral half of the chain, the blood-vessel response. If the weak link is upstream, in desire and arousal itself, the chemistry runs through dopamine and the brain's melanocortin pathway, which blood-flow support never touches.

Centrally acting options exist: apomorphine, a dopamine agonist studied for erection initiation, and bremelanotide, better known as PT-141, studied for its action on the melanocortin pathway of desire. algorx offers several as compounded formulations, prescribed case by case by independent licensed providers and filled by licensed partner pharmacies.

Choose with open eyes: compounded products are not FDA-approved, algorx does not manufacture or compound them, and the evidence for the central agents in men is thinner and earlier-stage than the mountain of trials under the PDE5 class.

The pattern across all of it: the fix for a failed pill is almost never a louder funnel selling the same pill. It's a person qualified to find the weak link in your chain, and the patience to adjust from there.

What Actually Helps: From Root-Cause Workup to the Right Treatment

What blood tests matter when you have ED? Exactly one is guideline-anchored for every man, the early-morning testosterone draw; the rest are the clinician's call, case by case. A real evaluation, per the AUA, covers the man's medical, sexual and psychosocial history, a physical exam, and lab testing chosen selectively, selective being the operative word. In practice, blood tests for erectile dysfunction stack like this:

• For everyone: the morning testosterone draw, confirmed with a second if low.

• Commonly added: fasting glucose or A1c and a lipid panel when recent results don't exist.

• Case by case: LH, then prolactin when testosterone and LH both run low; a TSH when the picture suggests thyroid; kidney and liver basics when history warrants.

Alongside the labs sits a five-question score, the SHIM questionnaire, validated against clinical diagnosis and used to grade severity and track whether treatment is working.

On treatment, the guideline's stance is that every man should hear about all options not contraindicated for him, and that the choice belongs to him, his partner where relevant, and his clinician together. The menu is wider than one pill: the PDE5 class, with durations that differ by molecule; counseling for the psychological loop; treating the underlying condition; mechanical and surgical routes for the hard cases.

Lifestyle sits underneath it all, and exercise trials show measurable gains in erectile scores, biggest in men who started worst. One boundary before you spend money: shockwave therapy and stem cells remain investigational, and PRP experimental, per the AUA; a Mayo urologist's phrasing is that they're not ready for prime time.

If you'd rather walk in with numbers than adjectives, comprehensive bloodwork through algorx covers the panels above, as full packages or individual markers. Labs and medication evaluations are separate workflows: you can order a panel without ever requesting medication, no medication request needs labs first, and the results come to you rather than through a clinician's read, so bring them to your provider or PCP. Knowing your baseline is how you tell a real indication from a hunch.

How algorx Approaches ED

algorx was built for the four-system version of ED this article describes, and the process is shaped accordingly. The whole path:

1. You pick the medication, or the lab panel, you came for.
2. You answer a brief online medical questionnaire; this is the history-taking step, because the cause matters.
3. An independent licensed provider reviews it, typically within 24 to 48 hours, and prescribes only where appropriate.
4. A licensed partner pharmacy fills it. FDA-approved generic tadalafil and sildenafil ship in 1 to 3 business days.

After you become a patient, secure messaging connects you to your provider, and that follow-up loop is where the fixes from the pills section happen: dose adjustments, timing corrections, honest check-ins. Pricing is visible before checkout, and the process takes two to three minutes, which is the part that should feel like ecommerce. The provider review is the part that shouldn't.

You're reclaiming a capability, and the earlier you act on what your body flags, the more there is to reclaim.

Two ways to start. If treatment is the move, tadalafil is available through algorx with pricing on the page. If you'd rather see your numbers first, comprehensive bloodwork is the other door. Either way: eligibility and state availability apply, an independent licensed provider makes every prescribing decision, and approval is never guaranteed.

The bottom line

ED isn't only about blood flow; it's a report from four systems, and every one of them is treatable. Vascular causes are real and often first. Nerves, hormones and the head each get a vote, usually more than one at once. And the signal is worth acting on early: caught in your 30s or 40s, ED can be the cheapest cardiovascular heads-up you'll ever get.

The outlook is good; this is a problem medicine treats well. The main gap between men who fix it and men who live with it is the decision to get evaluated. Start with treatment or start with your numbers, but start.

Dr. Adam Hotchkiss

Founder, algorx

Dr. Adam Hotchkiss is a doctor, healthcare entrepreneur, and founder of algorx. After completing a four-year foot and ankle surgical residency, he transitioned from clinical practice into performance-focused healthcare, helping build and lead modern telehealth organizations serving thousands of patients. At algorx, Dr. Hotchkiss combines his medical background with firsthand experience across bodybuilding, powerlifting, CrossFit, and other competitive disciplines to shape the company's clinical education, product strategy, and mission to help people Become More. Dr. Adam Hotchkiss has appeared on numerous leading health, fitness, and performance podcasts, including interviews with Mark Bell's Power Project, Dave Tate (EliteFTS), Fouad Abiad, and Simon Hill's The Proof, where he has discussed performance health, hormones, longevity, and evidence-based medicine. These interviews are publicly available on YouTube and other podcast platforms.

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