Erectile dysfunction medication isn’t working? Here’s why

There's no shortage of ED medication that works, and the research behind it is solid. So what happens when yours isn't?

How does erectile dysfunction treatment work?

At Numan, we offer four ED medications: sildenafil, Tadalafil Daily, tadalafil, and Viagra Connect. They're all classed as PDE5 inhibitors, which work by preventing the breakdown of cGMP, a molecule that lets the blood vessels in the penis relax and fill with blood.

In a large clinical trial of more than 8,000 patients, 82% reported improved erections after taking 100mg of sildenafil.¹ That's a strong success rate, but it also means the medication doesn't work as expected for around 1 in 5 people who try it, which is usually down to one of the reasons below.

1. You're taking it incorrectly

Each ED treatment should be taken in a specific way, with different expectations about how it works:

• Sildenafil: A tablet that should be taken one hour before you plan on having sex. The effects last for around four hours. This is your window of arousal. Sildenafil doesn't affect libido, so you still need to be sexually aroused for the treatment to be effective.¹

• Tadalafil Daily: A PDE5 inhibitor, taken daily so the effects are continuous. Many people choose it because it removes the need to plan sex within a specific time frame, and it's well suited to people who have sex regularly and prefer it to be less regimented. It takes around three to five days for the medication to build up and become effective.² After this, the effects are continuous.

• Tadalafil: Effective in as little as 30 minutes and can last for up to 36 hours.² It's more tolerable with food than sildenafil.

• Viagra Connect: Contains the active ingredient sildenafil, and works as described above.¹

2. You're eating a big meal beforehand

If you're taking sildenafil (this is the active ingredient in Viagra Connect), you're advised to wait a couple of hours after a large meal before taking the medication. Having a lot of food in your stomach significantly increases the time it takes for the medication to be absorbed, which could mean it's not working by the time you want it to.¹

When it comes to food and ED medications, it's also worth being wary of grapefruit. It contains compounds that interfere with how your body processes the medication, which could mean you experience heightened side effects.³

Tadalafil works slightly differently to sildenafil and can be taken with food. Tadalafil Daily is a low-dose medication that's taken every day and is more suitable for people who prefer less regimented sex.⁴

3. You're drinking too much alcohol

Alcohol is infamous for the harm it does to erections. Cutting down on alcoholic drinks means your body will be more naturally inclined to become erect when sexually aroused.⁵ Combined with ED medication, you have a better chance of success.

4. You've got a physical issue

Most ED treatments work by increasing blood flow to the penis, resulting in a stronger erection. But if you're sexually aroused and taking your medication correctly, and it's still not working, you may have a physical condition that doesn't respond as well to PDE5 inhibitors like sildenafil.

Nerve damage: Damage to the nerves can prevent the arteries around the penis from relaxing properly, which inhibits your ability to get an erection. This often happens after invasive procedures such as prostate surgery, and it can take longer for PDE5 inhibitors to become effective while the nerves recover.⁶

Hormonal imbalances: Low testosterone, which becomes more common with age, can reduce your libido, and ED medication doesn't affect arousal.⁷ An underactive thyroid can also interfere with the hormones that support healthy erections. A blood test can check both your testosterone and thyroid function.

5. You're not sexually aroused

Many people think that taking ED medication will instantly result in an erection. This isn't the case.

ED medications need a window of time to work, and you still need to be sexually stimulated during that window for them to be effective.¹ When you're aroused, your brain sends nerve signals that trigger the blood vessels around the penis to relax and fill with blood. This is the stage where PDE5 inhibitors like sildenafil and tadalafil step in. Without any stimulation, that first signal never happens, so the medication has nothing to work with.

There are various psychological reasons why you might be struggling to feel aroused, from body image issues to relationship problems, anxiety or depression.

If you're having relationship problems, it's worth speaking to your partner. Relate offers advice on sex and relationships, and charities such as Mind offer support for anyone struggling with anxiety or depression. You can also visit your local GP.

6. You need a higher dosage or different medication

If you're not seeing results on your current ED medication, there are alternative treatments and dosages that may work better for you. Speak to our clinical team about increasing your dosage or trying a different medication. If you're still not seeing results, you might be advised to take a blood test. This can help get to the bottom of what's causing your ED, and point you towards a treatment that actually works for you.

The numan take

Most ED medications are PDE5 inhibitors: they relax blood vessels and increase blood flow to the penis, but they don't boost libido, so sexual stimulation during the medication's window is still essential.¹ If you're taking it correctly and you're aroused, but it's still not working, the most common culprits are a big meal, too much alcohol, or timing.

If none of that explains it, an underlying physical or hormonal cause is worth ruling out, and a blood test can help. Whichever it turns out to be, there's usually a way to get your treatment working the way it should. Speak to our clinical team about your options, or explore other ways to treat ED if medication alone isn't cutting it.

References

^{1 Electronic Medicines Compendium. Sildenafil 100 mg film-coated tablets: Summary of Product Characteristics [Internet]. Datapharm; revised 11 Jun 2026 [cited 2026 Sep 30].}

^{2 Coward RM, Carson CC. Tadalafil in the treatment of erectile dysfunction. Ther Clin Risk Manag. 2008;4(6):1315–30.}

^{3 Jetter A, Kinzig-Schippers M, Walchner-Bonjean M, Hering U, Bulitta J, Schreiner P, et al. Effects of grapefruit juice on the pharmacokinetics of sildenafil. Clin Pharmacol Ther. 2002;71(1):21–9.}

^{4 Costa P, Grivel T, Gehchan N. Tadalafil once daily in the management of erectile dysfunction: patient and partner perspectives. Patient Prefer Adherence. 2009;3:105–11.}

^{5 Karunakaran A, Michael JP. The impact of Abstinence From Alcohol on Erectile Dysfunction: A Prospective Follow up in Patients With Alcohol Use Disorder. J Sex Med. 2022;19(4):581–9.}

^{6 Shridharani AN, Brant WO. The treatment of erectile dysfunction in patients with neurogenic disease. Transl Androl Urol. 2016;5(1):88–101.}

^{7 Kjaergaard AD, Marouli E, Papadopoulou A, Deloukas P, Kuś A, Sterenborg R, et al. Thyroid function, sex hormones and sexual function: a Mendelian randomization study. Eur J Epidemiol. 2021;36(3):335–44.}