Erectile dysfunction drugs
| Other names | sildenafil citrate, Viagra |
|---|---|
| Health risk | Mild |
| Addiction risk | Mild |
| Legal risk | Mild |
Several oral medications are available for treating erectile dysfunction (the inability to get or keep an erection). The four most common are sildenafil (Viagra), tadalafil (Cialis), avanafil (Stendra), and vardenafil (Levitra). These medications all improve blood flow to the penis when combined with sexual stimulation and are collectively known as phosphodiesterase 5 (PDE5) inhibitors. PDE5 inhibitors do not cause erections without sexual arousal, and do not increase arousal.
PDE5 inhibitors all work the same way, so they have similar effects, risks, and risk mitigation strategies. However, they differ in how quickly and how long they work:
| Drug | Common
brand name(s) |
Time to
take effect[1] |
Duration
of effect[1] |
Instructions[2] |
|---|---|---|---|---|
| Sildenafil | Viagra, Kamagra | 30-60 minutes | 4-5 hours | Take on an empty stomach before sex. High-fat foods and
alcohol increase time to take effect |
| Tadalafil | Cialis, Cialis Daily,
Adcirca |
30-45 minutes | 24-36 hours | Take with or without food before sex. Can also be prescribed
as a lower dose taken daily for continuous effect. |
| Avanafil | Stendra, Spedra | 15-30 minutes | 6-12 hours | Take with or without food before sex. |
| Vardenafil | Levitra, Staxyn | 30-60 minutes | 4-5 hours | Take on an empty stomach before sex. High-fat foods and
alcohol increase time to take effect |
Background
Mechanism of action
Oral erectile dysfunction medications increase blood flow (vasodilation) by inhibiting the enzyme phosphodiesterase 5 (PDE5).[3] They also inhibit PDE5 elsewhere in the body, particularly the lungs, and can cause systemic vasodilation.
Erections occur when spongy tissue in the penis (the corpora cavernosa and corpus spongiosum) fill with blood, expand, and become rigid. The erectile tissue is surrounded by smooth muscle that is tonically (usually) contracted, and the muscle must relax (vasodilation) for sufficient blood to enter the penis. During arousal, the body increases production of cyclic guanosine monophosphate (cGMP), a molecule that triggers smooth muscle relaxation. Sildenafil increases the amount of cGMP in the corpora cavernosa by protecting cGMP from degradation by PDE5. Sildenafil has a similar molecular shape to cGMP and can bind strongly to PDE5, blocking cGMP from entering the enzyme's active site.
Other medical uses
In addition to erectile dysfunction, sildenafil is used to treat pulmonary arterial hypertension (a type of high blood pressure) in men and women.[4]
Risks and mitigation
Low blood pressure
A common side effect of erectile dysfunction drugs is a drop in blood pressure. Symptoms of low blood pressure include:
- blurred or fading vision
- dizzy or lightheaded feelings
- fainting
- fatigue
- trouble concentrating
- upset stomach
Sitting up or standing can further lower blood pressure to the brain and make these symptoms more severe. Stopping physical activity and lying down can help reduce symptoms of low blood pressure, and also prevent falling injuries in case of fainting.
Painful, prolonged erection
In rare cases, a person taking an erectile dysfunction drug may experience a painful erection that continues for hours beyond sexual stimulation, known as priapism.[5] This is caused by blood not being able to leave the penis. Priapism is a medical emergency that requires immediate care to prevent permanent damage to the penis.[5]
Other side effects
Different erectile dysfunction drugs and their "fillers" can have different side effects. These will be listed in the notes from the pharmaceutical company that come with the prescription.
Drug interactions
Using erectile dysfunction drugs in combination with poppers or drugs that treat high blood pressure can cause a fatal drop in blood pressure. Starting with smaller doses of poppers can allow a person to gauge how their body responds to the mixture.
Drinking alcohol with erectile dysfunction drugs can make it more difficult to get an erection, but is recognized as safe by medical authorities.[6]
The UK NHS reports:[6]
It can also be dangerous to take sildenafil with:
- stimulants like MDMA (ecstasy) or cocaine
- hallucinogens like LSD
- novel psychoactive substances (which used to be known as legal highs) like mephedrone
Sildenafil has not been properly tested with recreational drugs.
Talk to your doctor if you think you might use any recreational drugs with sildenafil.
Known incidents
Medical case reports
RACKWiki incident reports
References
https://www.nhs.uk/conditions/low-blood-pressure-hypotension/
- ↑ 1.0 1.1 "Which drug for erectile dysfunction?". Harvard Health. 2014-05-12. Retrieved 2025-11-17.
- ↑ "What to know about oral meds for erectile dysfunction". Mayo Clinic. Retrieved 2025-11-17.
- ↑ "Sildenafil". go.drugbank.com. Retrieved 2025-11-06.
- ↑ "Sildenafil (oral route) - Side effects & dosage". Mayo Clinic. Retrieved 2025-11-06.
- ↑ 5.0 5.1 "A prolonged erection of the penis-Priapism - Symptoms & causes". Mayo Clinic. Retrieved 2026-03-01.
- ↑ 6.0 6.1 "Common questions about sildenafil". nhs.uk. 2022-03-03. Retrieved 2026-03-01.