How does Viagra work?

Written with

Amanda Barge

‍‘Phosphodiesterase 5’ (PDE5) inhibitors are ED pills taken to help men get an erection if they have erectile dysfunction.

PDE5 inhibitor drugs include:

Sildenafil (brand name: Viagra)
Tadalafil (brand name: Cialis)
Avanafil (brand name: Stendra)
Vardenafil (brand names: Levitra and Staxyn)

Although these famous pills are used by lots of men all over the world, not many of us actually know how they work.

That's because things get a little complex when understanding how these PDE5 inhibitors help with ED, so Urologist Ramesh Krishnan helps us break it down below.

Getting an erection

To get our heads around how ED pills work (and why they may or may not work for you), we need to start by understanding how men get erections.

The key parts to getting erect:

Your brain senses sexual arousal (this could be from physical touch or other mental stimulation like sight or thoughts)
Nerve signals are sent to the penis
These signals release chemicals (cGMP), which tell the muscles in the penis to relax
This allows the erectile bodies in the penis to fill with blood, and an erection is formed
Afterward, the PDE enzyme kicks in, to tell your erection to end

If you’d like to get more stuck into the science, read the sections below. If not, you can skip to the section about PDE5 inhibitors.

cGMP & smooth muscle relaxation:

cGMP gets the erection party started.

When someone is stimulated and becomes aroused, signals are sent from the brain to the penis, which releases a chemical called ‘cGMP’.

cGMP causes ‘smooth muscle relaxation’. In the penis, when smooth muscle cells relax, it allows more blood in, becomes hard, and an erection can form.

Erectile bodies in the penis & blood flow:

Your penis is a pretty amazing organ that can take on very different forms. One minute it can be floppy and relaxed, and the next minute it can be hard and excited.

It’s able to do this because of the parts of the penis called the ‘erectile bodies’:

‘Erectile bodies’ in the penis are made up of spongy tissue called ‘the corpora cavernosum’ and a stretchy covering called ‘the tunica’
When you get an erection, blood fills the spongy tissue in the penis
This allows it to get hard, and increases the length and girth of the penis
The stretchy covering then stretches and traps the blood in the spongy tissue
This stops the flow of blood out of the spongy tissue in the penis – helping you to maintain your erection

PDEs & your erection going down:

Once you’ve climaxed (or you’re just not feeling aroused anymore), ‘Phosphodiesterases’ (PDEs) close the erection party down.

PDEs are enzymes that break down cGMP and signal for your erection to switch off, and for normal life to resume. Once they’ve done their job, blood will flow out of the penis and the smooth muscle cells will go back to normal.

Without PDEs, men would be walking around with erections all the time. Awkward.

PDE5 inhibitors

PDE5 inhibitors work in 2 ways:

1. Getting an erection

PDE5 inhibitors block signals from the PDE enzyme, which allows more cGMP to hang around for longer (remember, cGMP is what causes smooth muscle relaxation, which leads to increased blood flow).

Therefore, in short, PDE5 inhibitors help smooth muscle relaxation occur.

This leads to ‘vasodilation’ (the smooth muscle relaxation allows for the blood vessels to widen, which increases blood flow around the body, including to the erectile bodies in the penis).

So, they can help men get an erection.

2. Keeping an erection

The increased blood flow from taking PDE5 inhibitors leads to a firmer and harder erection.

A firmer, harder erection stretches the tunica more, helping to trap in the blood.

So, this allows the erection to last longer, as less blood escapes out.

Erectile dysfunction (ED) & PDE5 inhibitors

If you have ED, your body or brain might block the natural part of the erection process, and won’t send the blood to the penis (which we now know is needed to get erect).

PDE5 inhibitors were designed for physical ED, but not for psychological ED. We’ll explain why below.

Physical ED

PDE5 inhibitors can be used to help physical ED stemming from anything that has hindered blood flow, regardless of the root cause.

Blood flow to the penis can be affected by many different diseases, including:

Heart disease
Diabetes
Renal insufficiency (poor function of the kidneys)
Hypertension (high blood pressure)
A neurological disease (resulting from damage to the brain, spine, or nerves)

Decreased blood flow can also be from:

A blockage (such as plaque build up in the heart or high cholesterol)
Stiffness of the arteries so they don’t relax as well (this also causes high blood pressure)
Nerve damage to nerves that supply smooth muscle (this can be common after prostate surgery)
Medications used for some of these conditions (such as blood pressure medications)

Think of PDE5 inhibitors as watering a wilted plant when it’s dry. Or an hour of phone charge when the battery is low. They don’t perform any magic on blood flow, but they can boost the natural chemical process needed to improve erections.

“So, they can give you a one-off erection, but they can’t treat the underlying cause – they simply help the symptoms of ED (not being able to get and stay hard). This means that unfortunately, as an underlying disease progresses, these ED medications can begin to stop working.”

Dr Ramesh Krishnan, Urologist

Psychological ED

PDE5 inhibitors weren’t created for men with psychological erectile dysfunction because men with psychological ED don’t usually have an underlying blood flow issue, which is what ED pills were built for.

“When you have sexual performance anxiety or you’re feeling stressed, your body can go into ‘fight or flight’ mode. This is a response from our caveman days that gets you ready to run away from danger or fight for your life.”

‍Amanda Barge, Psychosexual and Relationship Therapist

Unsurprisingly, when your body is in this state, getting an erection isn’t a priority, so blood is sent to your brain and muscles, and not to your penis. So, if your erectile dysfunction is caused by something psychological like anxiety or stress, taking ED pills that widen the blood vessels in the penis won’t have the desired effect.

“PDE5 inhibitors can actually be detrimental for men with psychological ED because if they do work (placebo effect) the patient may become dependent on them. And if they fail – which is most of the time – it can even worsen the underlying psychological issue.”

Dr Ramesh Krishnan, Urologist

Also, importantly, PDE5 inhibitors won’t suddenly give you an erection. You have to be sexually aroused for the brain to send the right chemical messages in the first place to make the erection process happen. And, often, a decrease in libido (sex drive) can be a psychological cause of ED, which can get in the way of these chemical messages.

What next?

To figure out if your erectile dysfunction is caused by a physical blood flow issue, then speak to your doctor, who can diagnose you and get you the right treatment (which may include a prescription of ED pills).

If your erection issues are caused by something psychological, Mojo is a pill-free solution and could help you get better erections and feel more confident in bed. Find out if Mojo is right for you by taking our quiz today.

Mojo aims to provide useful wellbeing resources to its users; however, you should not solely rely on opinions or advice available on the Website or given by the Community. Always seek advice from a qualified medical doctor or other healthcare professional before acting.