Erectile dysfunction, explained.
How an erection works, where the medications act, why timing matters, and why a provider checks your heart before prescribing anything. From the labeling and the urology guidelines.
Written from FDA labeling, clinical guidelines and the studies cited below. Educational, not medical advice, and not a substitute for talking with a licensed provider. Updated September 2026.
It is common, and it is physical.
About half of men aged 40 to 70 in the Massachusetts Male Aging Study reported some degree of erectile difficulty. Blood flow, nerves and hormones are usually involved, not just nerves of the other kind.
Blood flow is the mechanism.
Arousal releases nitric oxide, which makes a molecule called cGMP that relaxes the muscle inside the penis so blood can fill it. An enzyme called PDE5 breaks cGMP down.
The medicines need a signal.
Sildenafil and tadalafil block PDE5, so cGMP lasts longer. They work with arousal, not instead of it: no signal, no effect.
It can be a warning light.
The arteries that feed an erection are small, so they often show trouble years before the heart does. That is why a provider asks about your heart, and why nitrates are a hard no.
The facts, at a glance.
of men aged 40 to 70 reported some degree of erectile dysfunction in the Massachusetts Male Aging Study
is the window sildenafil's FDA labeling describes; tadalafil's describes up to 36 hours
before is the timing sildenafil's labeling suggests; a high-fat meal delays it
Timing, compared.
The two medications differ mainly in when you take them and how long the window lasts. Figures are from the labeling for the FDA-approved products. Tap an option.
Taken about an hour before. The window runs up to about four hours. A heavy or high-fat meal slows absorption, so timing around dinner matters. Arousal still has to happen.
Never with nitrates or riociquat. Which medication, and how you use it, is your provider's call. Nothing you tap here is stored or sent.
What happens, and where the medication steps in.
Five steps, one enzyme, and a medication that changes the balance for a few hours or a day and a half.
- 1Arousal
Sexual stimulation, physical or mental, sends nerve signals to the penis. Without this step nothing below happens, medication or not.
- 2Nitric oxide
Nerve endings and the vessel lining release nitric oxide, which triggers production of cGMP inside the smooth muscle.
- 3Muscle relaxes, blood fills
cGMP relaxes the muscle, arteries open, blood fills the spongy tissue, and the outflow veins are compressed shut.
- 4PDE5 winds it down
The enzyme PDE5 breaks down cGMP, muscle tightens, blood leaves. This is the normal off switch.
- 5Where the medication acts
Sildenafil and tadalafil block PDE5, so cGMP stays around longer and the response to arousal is stronger and lasts. Nitrates raise the same pathway, which is why the two together can crash blood pressure.
Who it is for, and who it is not.
Usually a fit
- Adults with erectile difficulty, evaluated by a licensed provider who reviews heart health and medications
- Able to describe what happens and when, so the provider can pick the medication and timing that fit
- Willing to report anything unusual right away
Not a fit, or needs a closer look
- Anyone taking nitrates (nitroglycerin, isosorbide) or riociguat: the combination can drop blood pressure to dangerous levels
- Heart conditions that make sexual activity itself unsafe: your provider assesses this first
- A recent heart attack or stroke, severe liver or kidney disease, or a history of NAION (a sudden optic nerve problem) or retinitis pigmentosa: provider review
- Anyone under 18
A licensed provider makes every prescribing decision from your health history and, where required, your labs. Not everyone is approved, and if you are not, you are refunded in full.
What the first months look like.
- Day 0Intake and review
A short online visit covering your health, heart history and every medication you take. A US-licensed provider reviews it, usually within an hour or two.
- DaysFirst shipment
The pharmacy prepares your order in 1 to 2 business days on average, then it ships next-day air in plain packaging.
- First useTiming
Sildenafil is taken about an hour before, and a heavy or high-fat meal delays it. Tadalafil is more flexible and lasts longer. Arousal still has to happen. A first try is not always the best try; labeling notes it can take a few.
- OngoingRefills and check-ins
Refills ship automatically. Message your care team about side effects or timing. An erection lasting more than four hours is an emergency; sudden loss of vision or hearing means stop and seek care.
What we offer for this.
Every treatment starts with a $0 online visit and ships free, in plain packaging, from a licensed US pharmacy. Prescription only, at the provider's discretion.
A different approach to desire.
The PDE5 inhibitor known for its long window: up to 36 hours as needed, or a steady low daily dose.
The original PDE5 inhibitor and the classic as-needed option for erectile dysfunction, working within 30 to 60 minutes.
Ask the concierge.
An automated guide to these treatments, one tap at a time. Not a real person and not a doctor; a licensed US provider makes every treatment decision.
Loading the guide. If it does not appear, the treatments are listed above.
The questions people actually ask.
Sildenafil or tadalafil?+
Are these the FDA-approved medications?+
Can I drink alcohol?+
Is ED a sign of low testosterone?+
What if it does not work?+
Where this comes from.
- Feldman et al., Massachusetts Male Aging Study: impotence and its medical and psychosocial correlates (1994) (opens in a new tab)
- American Urological Association, Erectile Dysfunction guideline (opens in a new tab)
- American Heart Association, Sexual Activity and Cardiovascular Disease (scientific statement) (opens in a new tab)
- DailyMed, sildenafil tablet labeling (opens in a new tab)
- DailyMed, tadalafil tablet labeling (opens in a new tab)
Written from FDA labeling, clinical guidelines and the studies cited below. Educational, not medical advice, and not a substitute for talking with a licensed provider. Compounded medications offered by Freedom RX are prepared by state-licensed 503A pharmacies for an individual prescription; they are not FDA-approved and have not been evaluated by the FDA for safety, effectiveness or quality. For a medical emergency, call 911.
Ready to get personalized treatment?
Start your online visit. It takes about five minutes, and if a provider does not approve your treatment you are refunded in full.