Tadalafil and Phenelzine: Can They Be Taken Together?
Learn about the interaction, what your prescriber checks, and how to use ED treatment safely.
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Tadalafil and Phenelzine: Understanding the Interaction
Published: 24 October 2026
Many men wonder whether tadalafil and phenelzine can be taken together safely. Tadalafil is a PDE5 inhibitor used to treat erectile dysfunction, while phenelzine is a monoamine oxidase inhibitor (MAOI) antidepressant. Although no major direct pharmacological interaction between these two medicines is commonly reported in standard references, both can affect blood pressure, and the combination requires careful assessment by a prescriber who will review your full medical history and current medications [2][3][4].
Key takeaways
- No major direct interaction is reported between tadalafil and phenelzine, but both can lower blood pressure.
- A prescriber must review your full medical history before approving tadalafil if you take phenelzine.
- Watch for dizziness when standing and avoid heavy alcohol while taking both medicines.
- Always declare all medications, including antidepressants, in your online consultation.
- New ED should be discussed with your GP, as it may signal underlying health conditions.
What Is Tadalafil and How Does It Work?
Tadalafil is a prescription medicine licensed in the UK for erectile dysfunction (ED). It belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors [4]. When you are sexually stimulated, tadalafil helps increase blood flow to the penis by relaxing the blood vessels, making it easier to get and keep an erection suitable for sexual activity [1].
Tadalafil is available in two forms: on-demand tablets (usually 10 mg or 20 mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) and daily low-dose tablets (2.5 mg or 5 mg taken once a day) [4]. The medicine does not work without sexual stimulation and does not cure ED or increase sexual desire. It is sold under the brand name Cialis and as generic tadalafil.
Common side effects include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. Tadalafil can lower blood pressure slightly, which is usually not a problem for most men but becomes important when combined with other medicines that also affect blood pressure [3][4].
What Is Phenelzine and Why Is It Prescribed?
Phenelzine is a monoamine oxidase inhibitor (MAOI), a type of antidepressant used to treat depression, particularly when other antidepressants have not worked. MAOIs work by blocking the enzyme monoamine oxidase, which breaks down certain chemical messengers in the brain such as serotonin, norepinephrine, and dopamine. By preventing this breakdown, phenelzine increases the levels of these mood-regulating chemicals.
Phenelzine is less commonly prescribed today because it requires strict dietary restrictions (avoiding foods high in tyramine, such as aged cheese, cured meats, and certain fermented products) and has the potential for serious interactions with other medicines and foods. It can also affect blood pressure: MAOIs may cause postural hypotension (a sudden drop in blood pressure when standing up), but they can also cause dangerous rises in blood pressure when combined with certain substances.
Because of these complexities, phenelzine is usually reserved for people with treatment-resistant depression and is prescribed under specialist supervision. If you are taking phenelzine, your doctor will have discussed the dietary and medication restrictions with you in detail.
Depression and Erectile Dysfunction
Depression itself is a common cause of erectile dysfunction, and many antidepressants can also contribute to sexual difficulties as a side effect [1][2]. This creates a challenging situation: the condition being treated and the treatment itself may both affect sexual function. If you are experiencing ED while taking an antidepressant, it is important to discuss this with your GP rather than stopping your medication, as untreated depression can worsen ED and overall quality of life.
At a glance
The Interaction Between Tadalafil and Phenelzine: What We Know
There is no well-documented direct pharmacological interaction between tadalafil and phenelzine in standard UK prescribing references [3][4]. This means that tadalafil does not significantly affect how phenelzine works, and phenelzine does not substantially alter the way the body processes tadalafil through the usual metabolic pathways.
However, both medicines can affect blood pressure. Tadalafil causes mild vasodilation (widening of blood vessels) and can lower blood pressure slightly [4]. Phenelzine, as an MAOI, is known to cause postural hypotension, particularly when you stand up quickly. When two medicines that can both lower blood pressure are taken together, there is a theoretical risk of additive effects—meaning dizziness, light-headedness, or fainting could be more likely, especially when changing position.
Because of this potential additive effect on blood pressure, and because phenelzine is a specialist medicine with complex interactions, any man taking phenelzine who wishes to use tadalafil must have this combination reviewed by a prescriber. The prescriber will assess your blood pressure, review all your current medicines, check for any other risk factors, and determine whether tadalafil is suitable and at what dose. You should never take tadalafil (or any ED medicine) without declaring that you are on phenelzine.
What Your Prescriber Will Check Before Approving Tadalafil and Phenelzine Together
When you request tadalafil through Cured Pharmacy's online consultation, you will be asked detailed questions about your current medications, including antidepressants. If you are taking phenelzine, the UK-registered prescriber reviewing your consultation will pay particular attention to several factors before deciding whether tadalafil is safe for you.
The prescriber will check your current blood pressure and whether you have experienced dizziness, fainting, or postural hypotension while on phenelzine. They will review your cardiovascular health, including any history of heart disease, stroke, or other conditions that might make the blood-pressure-lowering effect of tadalafil more significant. They will also confirm that you are not taking any other medicines that are absolutely contraindicated with tadalafil, such as nitrates, nicorandil, riociguat, or other PDE5 inhibitors [3][4].
The prescriber may recommend starting with the lowest effective dose of tadalafil to minimise the risk of side effects. They will also advise you on warning signs to watch for and when to seek medical help. This careful, individualised assessment is why all ED medicines at Cured Pharmacy require a clinical consultation—even though no major direct interaction is reported, your overall safety depends on reviewing your unique medical situation [2].
Why You Must Declare All Medications
It is essential to list every medicine you take—prescription, over-the-counter, herbal, and recreational—in your consultation. Some interactions are life-threatening (for example, tadalafil with nitrates), while others require dose adjustments or additional monitoring. Incomplete information can lead to unsafe prescribing, so always be honest and thorough when completing your medical questionnaire.
Always Stand Up Slowly
Both phenelzine and tadalafil can cause dizziness when you stand up. Take your time getting out of bed or up from a chair, especially in the morning, to reduce the risk of feeling light-headed or fainting.
Practical Advice: Taking Tadalafil While on Phenelzine
If your prescriber approves tadalafil while you are taking phenelzine, follow their instructions carefully. Take tadalafil exactly as prescribed—do not take more than the recommended dose or take it more often than once a day (for on-demand tablets) [4]. If you are prescribed the daily low-dose form, take it at the same time each day.
Be aware of the risk of dizziness or light-headedness, particularly when standing up from sitting or lying down. This is already a known side effect of phenelzine, and tadalafil may add to it. Stand up slowly, especially in the morning or after meals. Avoid heavy alcohol, as it can worsen both erectile dysfunction and low blood pressure, and can interact dangerously with phenelzine.
Continue to follow the dietary restrictions required for phenelzine (avoiding tyramine-rich foods) and do not stop or change your antidepressant dose without consulting your doctor. If you experience severe dizziness, fainting, chest pain during sex, or an erection lasting more than four hours, seek urgent medical help. Always inform any healthcare professional treating you (including in A&E) that you are taking both phenelzine and tadalafil.
Other ED Treatment Options and Tadalafil Alternatives
If tadalafil is not suitable for you while taking phenelzine, or if you experience side effects, other PDE5 inhibitors may be considered, such as sildenafil (Viagra), vardenafil (Levitra), or avanafil (Spedra) [3][5][6]. These medicines work in a similar way to tadalafil and have the same potential to lower blood pressure, so the same precautions apply. Your prescriber will help you choose the most appropriate option based on your individual circumstances.
Non-tablet treatments are also available. Eroxon is a topical gel that can be purchased without a prescription and works by creating a cooling then warming sensation to stimulate blood flow locally. Prescription options include Vitaros (alprostadil cream applied to the tip of the penis) and Caverject (alprostadil injection into the penis) [7]. These local treatments do not have the same systemic blood-pressure effects as PDE5 inhibitors, though they have their own side effects and suitability criteria.
It is also important to address the underlying causes of ED. If depression or the side effects of phenelzine are contributing to your erectile difficulties, discuss this openly with your GP or psychiatrist. Sometimes adjusting the antidepressant dose, switching to a different antidepressant (under specialist guidance), or adding psychological therapy can improve both mood and sexual function [1][2]. Lifestyle changes—such as regular exercise, stopping smoking, reducing alcohol, and managing weight—can also make a significant difference.
When to See Your GP
New or worsening erectile dysfunction should always be discussed with your GP, as it can be an early warning sign of cardiovascular disease or diabetes [1][2]. If you are already taking phenelzine and develop ED, do not assume it is only due to the antidepressant—other treatable causes may be present. Your GP can arrange tests, review your medications, and refer you to a specialist if needed.
When to get urgent help
- Erection lasting more than 4 hours (priapism)—go to A&E immediately
- Sudden loss of vision or hearing—stop tadalafil and seek urgent medical help
- Chest pain during or after sex—call 999; do not take nitrate sprays if you have used tadalafil
- Severe dizziness, fainting, or collapse—seek same-day medical assessment
- Signs of a hypertensive crisis (severe headache, confusion, chest pain) if you have eaten tyramine-rich foods—call 999
Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.
Scientific References
- NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 24 October 2026]
- National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 24 October 2026]
- Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 24 October 2026]
- Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 24 October 2026]
Information on this page is for educational purposes only and is not medical advice. Prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting or changing any medication.
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Common Questions
Can't find your answer? Our UK pharmacists review every consultation and can help.
Can I take tadalafil if I'm on phenelzine?
There is no major direct interaction reported, but both medicines can affect blood pressure. A prescriber must review your individual circumstances, blood pressure, and overall health before approving tadalafil.
Will phenelzine make tadalafil less effective?
Phenelzine does not reduce the effectiveness of tadalafil through drug metabolism. However, depression and some antidepressant side effects can contribute to erectile dysfunction independently.
What are the risks of taking tadalafil and phenelzine together?
The main concern is an additive effect on blood pressure, which may increase the risk of dizziness or light-headedness, especially when standing. Your prescriber will assess this risk before prescribing.
Do I need to tell my prescriber I'm taking phenelzine?
Yes, absolutely. You must declare all current medications, including antidepressants, in your online consultation. This ensures safe prescribing and appropriate dose selection.
Can I switch from phenelzine to another antidepressant to make ED treatment easier?
Never stop or change phenelzine without specialist advice, as MAOIs require careful withdrawal and switching protocols. Discuss any concerns about sexual side effects with your GP or psychiatrist first.
Are there ED treatments that don't interact with phenelzine?
Topical treatments like Eroxon gel or prescription alprostadil (Vitaros cream or Caverject injection) work locally and do not have the same systemic blood-pressure effects, though they have their own suitability criteria.
What should I do if I feel dizzy after taking tadalafil with phenelzine?
Sit or lie down immediately. If dizziness is severe, persistent, or accompanied by fainting or chest pain, seek urgent medical help and tell the healthcare professional you are taking both medicines.
How long does tadalafil stay in my system if I'm on phenelzine?
Tadalafil can remain active for up to 36 hours. Phenelzine does not significantly change how quickly your body clears tadalafil, but the blood-pressure effects of both medicines should be considered throughout this period.
Medically reviewed by
Tarun Kumar, Superintendent Pharmacist (GPhC 2233073)