Most people have heard that tadalafil and nitrates do not mix. Far fewer know about a second, newer “never together” partner: riociguat. It is a specialist medicine for two forms of pulmonary hypertension, so it rarely appears on the average household shelf. But when it does, it appears in people who are often also prescribed, or tempted to ask about, a PDE5 inhibitor. That includes tadalafil for erectile dysfunction, and tadalafil’s own pulmonary hypertension versions.
This article follows the journey of a patient and a pharmacist through three stages: before either drug is started, during treatment, and after a change of therapy. Looking at the topic by stage makes the pharmacist’s role easier to see. It also covers the specific question patients ask most often: “if I am switching between these drugs, how long do I have to wait?”
Quick answer: Tadalafil and riociguat must not be taken together. The U.S. prescribing information for riociguat lists use with PDE5 inhibitors as a contraindication, and tadalafil labels carry the matching warning. Switching from one to the other requires a washout period set by the treating specialist: the riociguat label calls for stopping tadalafil at least 48 hours before the first riociguat dose, and stopping riociguat at least 24 hours before any PDE5 inhibitor.
Understanding the two drugs: same pathway, different entry points
Blood vessels relax when a messenger called cyclic GMP (cGMP) builds up inside the muscle cells of the vessel wall. Cells make cGMP using an enzyme called soluble guanylate cyclase (sGC), and they break it down using phosphodiesterase type 5 (PDE5). Different drugs target different steps:
- Riociguat (Adempas) is an sGC stimulator. It makes the production enzyme more sensitive to the body’s own nitric oxide and also stimulates it directly, so more cGMP is made.
- Tadalafil is a PDE5 inhibitor. It blocks the breakdown enzyme so that cGMP persists longer.
Think of a bathtub: riociguat opens the tap wider, and tadalafil partly blocks the drain. Each is useful alone, and each is dosed on the assumption that the other is not adding to its effect. Both together can fill the tub far past the rim, which in the body means sudden, severe low blood pressure with fainting or worse. The riociguat label states plainly that use with PDE inhibitors, including sildenafil, tadalafil and vardenafil, is contraindicated, and the same applies to nitrates (Adempas prescribing information).
Who actually takes riociguat?
Riociguat is approved for adults with pulmonary arterial hypertension (PAH) and for chronic thromboembolic pulmonary hypertension (CTEPH) that persists or recurs after surgery or cannot be operated on. Both conditions involve raised pressure in the arteries of the lungs, which strains the right side of the heart and causes breathlessness, fatigue and reduced exercise tolerance. It is taken three times a day, with doses adjusted slowly under specialist supervision, and is often dispensed through specialty pharmacies that track the treatment closely.
Tadalafil also has a pulmonary hypertension role. Versions marketed for PAH are prescribed at different doses from the ED products, and an oral suspension exists for people who cannot swallow tablets. This means a patient might hold riociguat from a pulmonary hypertension clinic and meet tadalafil through a second route (urology, a telehealth service or a friend’s supply). It is the cross-over between those worlds that causes trouble.
Stage one: before either drug is started
What the specialist and pharmacist check at the start
If you are about to begin riociguat, the team will confirm you are not taking any PDE5 inhibitor, nitrate or other drug acting on the same pathway. If you are about to begin tadalafil and you have pulmonary hypertension, they will confirm that riociguat is not part of the plan. The checks include:
- A complete list of current medicines, including ED treatments, prostate treatments, heart medicines, inhalers and supplements.
- PDE inhibitors beyond the famous ones. The riociguat label also lists non-specific PDE inhibitors such as dipyridamole and theophylline in its warning about hypotension, so a pharmacist may ask about asthma or blood-thinning medicines you take.
- Nitrates in every form. Riociguat is contraindicated with nitrates and nitric oxide donors, including recreational “poppers.” See our guide to tadalafil and isosorbide mononitrate for how the nitrate rule works.
- Other sGC stimulators. Riociguat is also contraindicated with other drugs in its class, such as vericiguat, which is used in heart failure.
- Pregnancy status for people who can become pregnant. Riociguat carries a boxed warning for embryo-fetal toxicity, so pregnancy must be excluded and contraception arranged before treatment begins.
- Interacting enzyme inhibitors. Strong CYP and P-gp/BCRP inhibitors, such as certain antifungals and HIV medicines, raise riociguat levels and may call for a lower starting dose.
- Blood pressure at baseline. Riociguat should not be started when blood pressure is already low, because its vasodilating action can push it lower.
What you can do before the first dose
Bring all the packaging, not just the names you remember. If you take tadalafil from any source, say so even if it is an old supply or an “occasional” use. If you are a man with pulmonary hypertension who also lives with erectile dysfunction, flag that early, because it shapes which ED options are realistic.
Stage two: during treatment
Why the danger does not fade with familiarity
People established on riociguat sometimes assume a one-off tablet of tadalafil could not do much. The evidence suggests otherwise. When riociguat was tested together with sildenafil in a phase 2 trial known as PATENT-PLUS, the combination led to a high rate of study discontinuation because of low blood pressure, and there were three deaths in the study, one assessed as possibly related to the combination. Regulators later cited that experience when they added riociguat-specific language to tadalafil’s safety information (European Medicines Agency scientific conclusions). That is a significant history for a pairing that sounds, on paper, like it might help two overlapping problems.
What a pharmacist keeps watching for
- New prescriptions from other clinicians. A urologist, primary-care doctor or online service may issue a PDE5 inhibitor without knowing about riociguat. The pharmacist is often the first to see both.
- Refill patterns. A sudden extra pharmacy or a gap in specialty refills can hint at a change in therapy that needs reconciling.
- Symptoms you report. Dizziness on standing, fainting, unusual headaches and a pounding heartbeat are all reasons to check the full medication list.
- Interacting drugs added later. Antifungals, HIV medicines and some other prescriptions can raise riociguat exposure and increase the hypotension risk.
What about erectile dysfunction while on riociguat?
This is a common and legitimate question. Pulmonary hypertension and its treatment can affect sexual function, and many men would like help. Because PDE5 inhibitors are off the table while on riociguat, the options are different. A pulmonary hypertension team, ideally with a urologist, can discuss approaches that do not use the same pathway, such as vacuum devices, injections, urethral therapies, counselling and attention to fatigue and breathlessness during intimacy. Our general guides on which erectile dysfunction drug is best and the safest drug for erectile dysfunction explain how the usual options compare, but the usual PDE5 choices are not available to you here, so use them as background only.
Stage three: after a change in treatment
This is where the arithmetic matters. A patient may legitimately move from a PDE5 inhibitor to riociguat, or occasionally the other way, under specialist direction. In these cases there must be a clear gap with no overlap. The riociguat prescribing information sets out the sequence:
| Move | What the label says | Why |
|---|---|---|
| From sildenafil to riociguat | Stop sildenafil at least 24 hours before the first riociguat dose | Sildenafil clears faster than tadalafil |
| From tadalafil to riociguat | Stop tadalafil at least 48 hours before the first riociguat dose | Tadalafil has a long half-life of about 17.5 hours in healthy adults |
| From riociguat to a PDE5 inhibitor | Stop riociguat at least 24 hours before starting the PDE5 inhibitor, then monitor for low blood pressure | Allows riociguat’s effect to wane first |
After any such transition, the label advises watching for signs and symptoms of hypotension. A pharmacist will usually build this into counselling: stand up slowly, report dizziness and avoid driving until you know how you react. Source details are in the Adempas prescribing information.
“Washout” is not DIY
These timings describe what a specialist applies to a planned switch. They are not an invitation to alternate drugs on your own, take tadalafil “on a night off” from riociguat, or time doses around a special evening. Riociguat is dosed three times daily, so a night off would itself be a treatment change with consequences for your lung disease. If you want to discuss switching, do it with your pulmonary hypertension specialist.
What if you took tadalafil while on riociguat by mistake?
Do not wait to see. Take these steps:
- Sit or lie down, preferably with your legs elevated, and avoid sudden standing.
- Contact your pharmacist, pulmonary hypertension clinic or an emergency advice line immediately. Provide names, doses and times for both drugs.
- Call emergency services if you feel faint, have chest pain, severe breathlessness, a very rapid heartbeat or confusion.
- Do not take other blood-pressure-lowering medicines or nitrates to “settle” your symptoms.
There is no specific antidote for the combination, so management is supportive and relies on early recognition. Being open with the clinical team about the mistake matters far more than any embarrassment.
Cross-checks that are easy to miss
Combination and “brand-switch” products
Prostate-symptom treatments that contain tadalafil, such as combinations with finasteride, are still tadalafil. If you hold such a product and begin riociguat, the same contraindication applies. The same is true if a doctor changes your sildenafil from a pulmonary hypertension brand to an ED brand: the molecule is the same. Our comparison of Revatio vs Viagra shows how one drug can wear several labels.
Telehealth and online sources
Online ED services often ask about “heart conditions” but may not ask about pulmonary hypertension or a specialist medicine like riociguat. Be proactive. If a questionnaire does not list your condition, write it in the free-text box, and consider telling the pharmacist directly.
Other drugs that act on cGMP
Beyond nitrates and PDE5 inhibitors, pharmacists pay attention to theophylline, dipyridamole and other PDE inhibitors that the riociguat label flags, as well as to combinations of vasodilating medicines more broadly. When you see a new prescription from any clinician, a brief pharmacist review is the cheapest safety step available.
Questions to ask your pharmacist or specialist
- Do any of my medicines, including inhalers and over-the-counter products, act on the same pathway as riociguat?
- If I want help with erectile dysfunction, which options are compatible with my pulmonary hypertension treatment?
- Who should I call if I accidentally take a PDE5 inhibitor?
- Do I have a written plan for what to do before any procedure, dental or surgical, that might involve nitrates?
- Could another pharmacy or provider be unaware of my riociguat prescription, and how can I fix that?
Living with pulmonary hypertension: practical habits for safer medicine use
Carry a medication card
Pulmonary hypertension is a condition most paramedics and emergency doctors see rarely. If you faint or become acutely breathless away from home, a card or phone note that says “I take riociguat three times daily; contraindicated with PDE5 inhibitors and nitrates” can influence the first treatment decisions. Include the dose, the time of the last dose, your specialist’s contact details and any allergies. It is a small piece of paper with an outsized effect.
Tell every clinician, every time
Dentists, podiatrists, urgent-care clinicians, travel-health nurses and surgeons often work from a short intake form that may not list a specialist drug. Say “riociguat” out loud and ask them to write it down. If anyone proposes a nitrate, a PDE5 inhibitor or another vasodilator, ask them to check with your specialist first. Most are grateful for the prompt.
Hospital stays and procedures
Hospitals use nitrates and vasodilating drugs routinely in cardiology, anaesthesia and intensive care. Because riociguat is a niche medicine, it is possible for an admitting team to overlook it. Before a planned procedure, ask your pulmonary hypertension team for written instructions about whether and when to pause riociguat, and which drugs to avoid in theatre and recovery. Keep that letter with your medication card.
Travel
If you travel, carry enough riociguat in the original packaging, along with a letter from your prescriber, and know the name of the nearest hospital with a pulmonary hypertension service. Do not buy “replacement” medicines abroad for erectile dysfunction or anything else without checking with a local pharmacist that you take riociguat and cannot use PDE5 inhibitors.
Counterfeit and online supplies: an extra layer of risk
Erectile dysfunction drugs are among the most counterfeited medicines in the world, and the problem is not limited to obscure websites. Tablets sold as “natural” boosters have been found to contain undeclared sildenafil, tadalafil or related compounds. For someone taking riociguat, an undeclared PDE5 inhibitor in a supplement is just as dangerous as a prescribed one, and it is much harder to spot because the label does not name it.
The safest policy is simple: if you take riociguat, do not use any product marketed for sexual performance, libido or “male enhancement” without a pharmacist reviewing the ingredient list, and be sceptical of any product with dramatic claims. Our article on how to spot fake Kamagra oral jelly shows how widespread counterfeit PDE5 products are, even in packaging that looks legitimate. Kamagra and similar products contain PDE5 inhibitors and are not an option for a person on riociguat.
A note for partners and caregivers
Pulmonary hypertension affects relationships as well as lungs. Breathlessness, fatigue and worry can reduce intimacy, and the drug restrictions can feel like one more loss. Partners and caregivers can help in several practical ways:
- Learn the names of the drugs your partner takes, including riociguat, and the fact that PDE5 inhibitors and nitrates are off limits.
- Discourage the borrowing of tablets between friends or family members. “It is only one pill” is the sentence that starts most accidents.
- Know the emergency plan: what symptoms mean calling an ambulance, where the medication card is kept and who the specialist team is.
- Encourage open conversation with the clinical team about sexual health. Specialists would rather hear about it than have patients try something unsafe on their own.
How pharmacists reconcile the lists
Medication reconciliation sounds technical, but it comes down to comparing every list that exists for you. A pharmacist handling a patient on riociguat may compare the specialty pharmacy’s record, the community pharmacy’s record, the hospital discharge summary and what the patient reports from memory. Discrepancies are common: a drug stopped by one clinician that is still on another’s list, a supply obtained elsewhere or a product never entered at all. Each gap is a place where an interaction can hide.
You can help by asking for a printed profile from each pharmacy you use, bringing all lists to appointments and updating them whenever anything changes. When a pharmacist asks “anything else, even over the counter or from abroad?” the most useful answer is a complete one.
Frequently asked questions
Can I take tadalafil one day and riociguat the next?
Not as an ad hoc pattern. Riociguat is dosed three times a day and its effect does not simply vanish overnight. Planned switches follow the label’s minimum gaps and are supervised by specialists. Skipping riociguat to take tadalafil can destabilise your lung disease and still carry risk.
Is tadalafil for pulmonary hypertension different from tadalafil for ED?
The active ingredient is the same, although doses and products differ. Both carry the riociguat contraindication because the risk comes from the drug’s action in the body, not the branding.
Does sildenafil have the same problem with riociguat?
Yes. In fact, the combination of sildenafil and riociguat was the one tested in the PATENT-PLUS trial that raised the alarm. For related background, see can you take Viagra and Cialis together, which explains why even two PDE5 inhibitors are not a pair to improvise with.
Do I need to avoid tadalafil forever once I stop riociguat?
Not necessarily. The label describes a minimum 24-hour gap after riociguat before a PDE5 inhibitor can be started, with monitoring for low blood pressure. Whether tadalafil is appropriate depends on your underlying condition and your specialist’s judgment.
What about alcohol?
Alcohol is an additional vasodilator and can add to dizziness and low blood pressure, particularly in people with pulmonary hypertension. Our article on Cialis and alcohol covers the tadalafil side of that story.
Can women be affected?
Yes. Riociguat is used by women and men, and tadalafil is used for pulmonary hypertension in both. The interaction rule is the same for everyone, and women of childbearing potential face the additional pregnancy-related requirements for riociguat.
Where can I read the official information?
Patient leaflets and prescribing information are published by regulators and manufacturers. One useful patient-facing option is the UK electronic leaflet for Adempas, which lists PDE5 inhibitors and nitrates among the medicines not to take with riociguat.
Bottom line
Tadalafil and riociguat are two drugs that work on the same blood-vessel signal and are never meant to be combined. The interaction can cause severe hypotension, and in a clinical trial of a related combination it led to serious harm. Your pharmacist checks at three points: before you begin either drug, throughout treatment as new prescriptions arrive, and after any planned switch to be sure the waiting periods were respected. The most protective thing you can do is make sure every clinician and pharmacy you use knows you take riociguat, and ask before you take anything that treats ED, prostate symptoms, pulmonary hypertension or chest pain.
Medical disclaimer: This article offers general information and is not a substitute for individual medical advice. Never start, stop or change a medicine without consulting your prescriber. If you have taken tadalafil and riociguat together and feel faint, short of breath or have chest pain, call emergency services immediately.