Erection medicines (PDE5 inhibitors)

They help more blood reach the penis during sexual arousal. They do not cause an erection by themselves and they do not increase desire.

What are they?

These medicines support erections by relaxing the blood vessels in the penis and increasing blood flow when there is sexual stimulation. They do not increase sexual desire.

Why are they used?

They may be useful to:

Improve erections during sex.
Counter difficulties linked to substance use.
Reduce performance-related anxiety.
Support longer sexual sessions.

The 4 most commonly used medicines

Medicine	Best-known brand name	Onset	Approximate duration
Sildenafil	Viagra®	30-60 min	4-6 hours
Tadalafil	Cialis®	30-60 min	Up to 36 hrs
Vardenafil	Levitra®	30-60 min	4-6 hours
Avanafil	Spedra®	15-30 min	6-8 hours

Duration refers to the time during which the medicine may help an erection if there is stimulation. It does not mean a continuous erection for that whole time.

Common side effects

Headache
Facial flushing
Nasal congestion
Dizziness
Heartburn or stomach discomfort
Muscle pain* (*more common with tadalafil)

Warning signs: seek urgent medical care

Severe chest pain
Trouble breathing
Fainting or loss of consciousness
Sudden loss of vision or hearing
Painful erection or one that lasts more than 4 hours (priapism)

Who should be especially careful?

People with a history of heart attack, stroke, or heart failure.
Very low or very high blood pressure that is not controlled.
People who take nitrates for the heart (nitroglycerin, isosorbide dinitrate).
Severe liver or kidney disease.
History of priapism.

How can they be taken more safely?

Respect the onset time. Do not take them too close to when you plan to have sex.
Take them with water. Avoid heavy alcohol use.
Avoid very heavy meals before taking them. They may delay the effect.
Know your health and your limits. If in doubt, talk with a professional.
If something feels wrong, stop the activity and ask for help.

Key harm reduction messages

Use the recommended dose. Do not take more than one dose because you think it “didn’t work.”
Sexual stimulation is needed for them to work.
Learn about interactions with substances before combining them.
Do not combine with nitrates (heart medicines) or poppers (inhaled nitrites).
If the erection lasts more than 4 hours, go to emergency care.

Remember

Duration refers to the period during which the medicine may help an erection if there is sexual stimulation. It does not mean the erection lasts for the whole time.

Note on how the medicines in this guide were selected

How did we choose the medicines included in this guide?

This guide does not aim to list every available medicine. Instead, it offers practical information on the treatments that are most relevant because of how often they are used and their interaction potential with psychoactive substances.

The medicines included were selected based on three criteria:

1. Frequent use in the populations this guide is for

Priority was given to medicines widely used by people living with HIV, people with viral hepatitis, PrEP and PEP users, and people who use medicines for erection or sexual performance.

2. Potential for clinically relevant interactions

Treatments were included when there is evidence of pharmacological or physiological interactions that may change effectiveness, increase the risk of adverse effects, or worsen toxicity when combined with psychoactive substances.

3. Relevance for harm reduction

Priority was given to medicines for which interaction information can help people make safer decisions, prevent complications, and support continuity of treatment.

Which medicines will you find in this guide?

Antiretroviral treatment for HIV (ART): includes the medicines and combinations most used in Latin America.
Pre-Exposure Prophylaxis (PrEP): medicines used to prevent HIV infection before exposure.
Post-Exposure Prophylaxis (PEP): medicines used after a possible HIV exposure to reduce the risk of infection.
Treatments for Hepatitis B and Hepatitis C: includes the most commonly used current treatments for these viral infections.
Erection medicines (PDE5 inhibitors): such as sildenafil, tadalafil, vardenafil, and avanafil.

A guide that evolves

Scientific evidence on pharmacological interactions changes constantly. For that reason, this guide will be updated regularly to include new medicines, new psychoactive substances, and the best available evidence.

The absence of a medicine or substance in this edition does not mean it is completely safe to combine, only that there is currently not enough evidence or that its use is uncommon in the populations this guide was designed for.

How should you use this information?

This guide does not replace consultation with healthcare professionals.
If you have questions about your medicines or your substance use, talk with your doctor or pharmacist.
Use this information to make more informed decisions and take care of your health and pleasure.
Share this guide with your friends and community.

Get informed, take care, and enjoy.

Reducing risks does not mean giving up pleasure. It means having more information to live your sexuality in a safer and more enjoyable way.

Interaction table: erection medicines and psychoactive substances

How do erection medicines interact with psychoactive substances?

This table shows the risk level of combining PDE5 inhibitors with psychoactive substances. Risk may vary depending on dose, frequency of use, your health status, and other medicines you take.

Risk level

Low: no clinically relevant interaction
Caution: mild risk, use carefully
Moderate: important risk
High: avoid the combination
Insufficient evidence

Substance	Sildenafil (Viagra®)	Tadalafil (Cialis®)	Vardenafil (Levitra®)	Avanafil (Spedra®)	Why does it happen? Main mechanism
Alcohol (any important amount)	Caution: lower blood pressure, dizziness	Caution: lower blood pressure, dizziness	Caution: lower blood pressure, dizziness	Caution: lower blood pressure, dizziness	Both may lower blood pressure and increase dizziness and fainting.
Cannabis	Caution: hypotension, dizziness, tachycardia	Caution: hypotension, dizziness, tachycardia	Caution: hypotension, dizziness, tachycardia	Caution: hypotension, dizziness, tachycardia	Cannabis may cause tachycardia and hypotension. It can enhance the vascular effects of PDE5 inhibitors.
Cocaine	Moderate: higher blood pressure, cardiovascular risk	Moderate: higher blood pressure, cardiovascular risk	Moderate: higher blood pressure, cardiovascular risk	Moderate: higher blood pressure, cardiovascular risk	Cocaine raises blood pressure, heart rate, and the risk of arrhythmia and heart attack.
MDMA / Ecstasy	Moderate: dehydration, hyperthermia, overexertion	Moderate: dehydration, hyperthermia, overexertion	Moderate: dehydration, hyperthermia, overexertion	Moderate: dehydration, hyperthermia, overexertion	Greater risk of cardiovascular strain, dehydration, and hyperthermia, especially during long sessions.
Methamphetamine	High: very high cardiovascular risk, priapism	High: very high cardiovascular risk, priapism	High: very high cardiovascular risk, priapism	High: very high cardiovascular risk, priapism	It strongly stimulates the cardiovascular system and prolongs sessions. It increases the risk of priapism and heart attack.
Ketamine	Caution: hypotension, dizziness, difficulty noticing injuries	Caution: hypotension, dizziness, difficulty noticing injuries	Caution: hypotension, dizziness, difficulty noticing injuries	Caution: hypotension, dizziness, difficulty noticing injuries	It may lower blood pressure and sensation, making it harder to recognise injury or pain.
GHB / GBL	Moderate: hypotension, drowsiness, fainting risk	Moderate: hypotension, drowsiness, fainting risk	Moderate: hypotension, drowsiness, fainting risk	Moderate: hypotension, drowsiness, fainting risk	Central nervous system depressants that may cause blood pressure drops and loss of consciousness.
Poppers (inhaled nitrites)	High: severe hypotension, loss of consciousness, heart attack, stroke	High: severe hypotension, loss of consciousness, heart attack, stroke	High: severe hypotension, loss of consciousness, heart attack, stroke	High: severe hypotension, loss of consciousness, heart attack, stroke	This combination may cause a sudden and dangerous drop in blood pressure. ALWAYS AVOID IT.
Opioids	Caution: drowsiness, hypotension	Caution: drowsiness, hypotension	Caution: drowsiness, hypotension	Caution: drowsiness, hypotension	They increase drowsiness and may worsen hypotension.
LSD	Insufficient evidence	Insufficient evidence	Insufficient evidence	Insufficient evidence	There are not enough studies. Use caution.
Inhalants	Insufficient evidence	Insufficient evidence	Insufficient evidence	Insufficient evidence	There are not enough studies. Use caution.

General recommendations

Use the lowest effective dose and wait at least 24 hours before repeating, except with avanafil (wait 12 hours).
Stay hydrated and rest if you expect long sexual activity.
Do not combine with poppers or nitrates (heart medicines).
If you feel chest pain, trouble breathing, intense dizziness, or blurred vision: seek immediate medical care.
Tell your healthcare team about your use patterns so you can receive non-judgmental guidance.

This information does not replace consultation with healthcare professionals. Every person is unique and risks can change.