Tadalafil drug interactions are not one homogeneous category. Organic nitrates and guanylate cyclase stimulators such as riociguat are contraindicated, while alpha-blockers, antihypertensive drugs and substantial alcohol intake can add to tadalafil's vasodilatory and blood-pressure-lowering effects.
A second major pathway involves pharmacokinetics. Tadalafil is metabolized predominantly by CYP3A4, so CYP3A4 inhibitors can increase tadalafil exposure and inducers can reduce it; other agents, such as some antacids, can affect absorption characteristics without necessarily changing total exposure.
This page is the master interaction hub. It explains how the major interaction classes differ and routes deeper questions to the nitrate, riociguat, alpha-blocker, alcohol and CYP3A4 pages rather than duplicating their detailed mechanisms.
The clearest way to interpret tadalafil interactions is to identify both the mechanism and the label consequence. A formally contraindicated combination is different from an additive blood-pressure interaction that calls for caution or a metabolic interaction that changes tadalafil exposure.
Current U.S. CIALIS labeling specifically addresses nitrates, alpha-blockers, antihypertensives, alcohol, CYP3A4 inhibitors and CYP3A4 inducers. Guanylate cyclase stimulators such as riociguat are separately included among formal contraindications.
The table below provides the hub-level interaction map and routes each major topic to the appropriate deeper page.
| Interaction class | Primary mechanism | Potential consequence | Label category | Read more |
|---|---|---|---|---|
| Organic nitrates | Additive nitric oxide/cGMP-mediated vasodilation | Potentially unsafe blood-pressure lowering | Contraindicated | Tadalafil and nitrates |
| GC stimulators such as riociguat | Enhanced cGMP signaling | Potentially unsafe hypotension | Contraindicated | Tadalafil and riociguat |
| Alpha-blockers | Additive vasodilation | Symptomatic hypotension, including fainting | Caution; indication-specific guidance | Tadalafil and alpha-blockers |
| Antihypertensive drugs | Additive blood-pressure lowering | Additional reduction in blood pressure | Interaction / precaution | Tadalafil and blood pressure |
| Substantial alcohol intake | Additive vasodilation | Orthostatic symptoms, dizziness and lower standing blood pressure | Interaction / warning | Tadalafil and alcohol |
| CYP3A4 inhibitors | Reduced tadalafil metabolism | Increased tadalafil exposure | Exposure interaction; potent inhibition triggers regimen-specific restrictions | Tadalafil and CYP3A4 |
| CYP3A4 inducers | Increased metabolic clearance | Reduced tadalafil exposure and potentially reduced efficacy | PK interaction | Tadalafil and CYP3A4 |
Pharmacodynamic interactions occur when another drug or substance adds to tadalafil's physiologic effect without necessarily changing tadalafil concentration. Nitrates, riociguat, alpha-blockers, antihypertensives and alcohol matter primarily because of overlapping effects on vascular signaling or blood pressure.
Pharmacokinetic interactions change how tadalafil is absorbed, metabolized or cleared. CYP3A4 inhibitors and inducers are the most important metabolic examples, while antacid studies illustrate that an absorption-rate change does not necessarily mean total systemic exposure changes.
This distinction helps explain why interaction management differs: one combination may be prohibited, another may require caution, and another may primarily change expected exposure or efficacy.
| Interaction type | What primarily changes? | Examples |
|---|---|---|
| Pharmacodynamic | Physiologic effect | Nitrates, riociguat, alpha-blockers, antihypertensives, alcohol |
| Pharmacokinetic — metabolism | Tadalafil exposure | CYP3A4 inhibitors and inducers |
| Pharmacokinetic — absorption | Absorption characteristics | Magnesium hydroxide / aluminum hydroxide antacid |
Current CIALIS labeling contraindicates tadalafil in patients using any form of organic nitrate, whether nitrate use is regular or intermittent. Tadalafil has been shown to potentiate the hypotensive effect of nitrates.
This is stronger than advice to simply monitor blood pressure or use caution. Routine concomitant use belongs to the formal do-not-use category.
The nitric oxide/cGMP mechanism, nitrate examples and label-supported timing context are intentionally reserved for the dedicated tadalafil and nitrates page.
| Nitrate interaction point | Current label interpretation |
|---|---|
| Regular organic nitrate use | Contraindicated |
| Intermittent organic nitrate use | Contraindicated |
| Primary concern | Potentiation of nitrate-induced hypotension |
| Simply separating routine doses | Does not replace the formal contraindication |
Tadalafil should not be used with a guanylate cyclase stimulator such as riociguat. Current labeling states that PDE5 inhibitors can potentiate the hypotensive effects of GC stimulators.
Nitrates and riociguat are different drug classes, so their mechanisms should not be treated as identical. What they share is the same high-level regulatory outcome with tadalafil: concomitant use is contraindicated.
The pathway-level explanation belongs on the tadalafil and riociguat interaction page.
| Question | Answer |
|---|---|
| Tadalafil + riociguat | Contraindicated |
| Primary concern | Potentiation of hypotensive effects |
| Same drug class as nitrates? | No |
| Same formal contraindication outcome? | Yes |
Tadalafil and alpha-adrenergic blockers are both vasodilators, so their blood-pressure-lowering effects can add together. In susceptible patients, clinically significant hypotension and symptoms such as fainting can occur.
Current labeling does not classify all alpha-blocker use as a blanket contraindication. For ED, patients should be stable on alpha-blocker therapy before tadalafil is initiated and tadalafil should begin at the lowest recommended dose; for treatment of BPH, tadalafil combined with an alpha-blocker is not recommended.
The hemodynamic evidence and indication-specific distinctions belong on the alpha-blocker interaction page.
| Clinical context | High-level label approach |
|---|---|
| ED + stable alpha-blocker therapy | Caution; tadalafil begins at the lowest recommended dose |
| Hemodynamic instability on alpha-blocker therapy | Greater risk of symptomatic hypotension |
| Tadalafil + alpha-blocker for BPH | Combination not recommended |
| All alpha-blocker use | Not a blanket formal contraindication |
Tadalafil is a mild systemic vasodilator and can augment the blood-pressure-lowering effect of antihypertensive medicines. Current CIALIS clinical pharmacology studies evaluated selected combinations with amlodipine, angiotensin II receptor blockers, bendrofluazide, enalapril and metoprolol.
The label reports small additional blood-pressure reductions in these studied settings rather than classifying routine antihypertensive therapy as a formal contraindication. Clinical relevance can still vary with baseline blood pressure, the number of antihypertensive medicines being used, intravascular volume and other patient factors.
The broader physiologic interpretation belongs on the tadalafil blood-pressure page.
| Studied antihypertensive example | General label finding |
|---|---|
| Amlodipine | Small additional blood-pressure reduction in the studied setting |
| Angiotensin II receptor blockers | Additive blood-pressure effect evaluated |
| Bendrofluazide | Additive blood-pressure effect evaluated |
| Enalapril | Additive blood-pressure effect evaluated |
| Metoprolol | Additive blood-pressure effect evaluated |
Alcohol and tadalafil both have vasodilatory effects. Current CIALIS labeling warns that substantial alcohol consumption, using approximately 5 units or more as an example, can increase the potential for orthostatic signs and symptoms.
Potential findings include increased heart rate, decreased standing blood pressure, dizziness and headache. In the cited interaction studies, tadalafil did not alter alcohol plasma concentrations and alcohol did not alter tadalafil plasma concentrations, so the main concern is additive physiology rather than a rise in drug levels.
The dose-context and practical interpretation belong on the tadalafil and alcohol page.
| Alcohol interaction feature | Interpretation |
|---|---|
| Primary mechanism | Additive vasodilation |
| Substantial intake example in labeling | Approximately 5 units or greater |
| Potential findings | Dizziness, headache, increased heart rate and reduced standing blood pressure |
| Alcohol raises tadalafil plasma concentration in the cited studies | No |
| Tadalafil raises alcohol plasma concentration in the cited studies | No |
Tadalafil is a CYP3A4 substrate and is metabolized predominantly through this pathway. CYP3A4 inhibition can increase tadalafil exposure, while CYP3A4 induction can lower exposure.
Current labeling includes ketoconazole and ritonavir among directly studied inhibitors and states that other inhibitors such as erythromycin, itraconazole and grapefruit juice would also be expected to increase exposure. Rifampin is the principal studied inducer, while carbamazepine, phenytoin and phenobarbital are expected to decrease tadalafil exposure.
The clinical implications differ by direction and strength of the interaction: potent inhibition triggers regimen-specific tadalafil restrictions, while induction can reduce exposure and may reduce once-daily efficacy. Quantitative AUC/Cmax changes, inhibitor strength and detailed dosing implications belong on the tadalafil and CYP3A4 page.
| CYP3A4 interaction | Examples | Expected tadalafil effect |
|---|---|---|
| Studied inhibition | Ketoconazole, ritonavir | Increased tadalafil exposure |
| Other expected inhibition | Erythromycin, itraconazole, grapefruit juice | Likely increased tadalafil exposure |
| Studied induction | Rifampin | Substantially reduced tadalafil exposure |
| Other expected induction | Carbamazepine, phenytoin, phenobarbital | Likely reduced tadalafil exposure |
Current CIALIS labeling specifically notes that once-daily use provides continuous plasma tadalafil levels. That ongoing exposure should be considered when evaluating interactions with nitrates, alpha-blockers, antihypertensives, potent CYP3A4 inhibitors and substantial alcohol consumption.
This does not mean every interaction becomes more severe with daily dosing, and it does not change a formal contraindication into an acceptable combination. It means interaction assessment cannot be based only on whether two substances were swallowed at the same moment.
The repeated-dose treatment framework itself belongs on the daily tadalafil page.
| Regimen feature | Interaction implication |
|---|---|
| As-needed tadalafil | Intermittent exposure |
| Once-daily tadalafil | Continuous plasma tadalafil exposure |
| Formal contraindication | Remains contraindicated regardless of regimen |
| Exposure-changing interaction | May require regimen-specific interpretation |
Not every pharmacokinetic interaction changes total tadalafil exposure. In current CIALIS labeling, simultaneous administration of a magnesium hydroxide/aluminum hydroxide antacid reduced the apparent rate of tadalafil absorption without changing total exposure measured by AUC.
Increasing gastric pH with the H2 antagonist nizatidine had no significant effect on tadalafil pharmacokinetics. These findings are useful because they distinguish a change in absorption rate from the much more consequential exposure increase seen with potent CYP3A4 inhibition.
A detected PK effect therefore needs to be interpreted by the parameter that actually changed rather than labeled generically as a dangerous interaction.
| Co-administered agent | Observed tadalafil PK finding |
|---|---|
| Magnesium hydroxide / aluminum hydroxide antacid | Reduced apparent absorption rate without changing AUC |
| Nizatidine | No significant effect on tadalafil pharmacokinetics |
Interaction assessment is bidirectional: another medicine can affect tadalafil, and tadalafil can also be evaluated for effects on other drugs. Current CIALIS labeling states that tadalafil is not expected to cause clinically significant inhibition or induction of clearance through the major cytochrome P450 isoforms tested.
Controlled studies found no significant tadalafil effect on warfarin exposure or warfarin-induced prothrombin-time changes, no significant exposure effect on midazolam or lovastatin and no significant steady-state pharmacokinetic effect on digoxin. Tadalafil also did not potentiate aspirin-associated prolongation of bleeding time in the cited study.
Theophylline provides a useful nuance: tadalafil did not significantly alter theophylline pharmacokinetics, although a small additional increase of about 3 beats per minute in heart rate was observed and its clinical significance was described as unknown.
| Drug / pathway studied | Current CIALIS label finding |
|---|---|
| Warfarin | No significant effect on S- or R-warfarin exposure or warfarin-induced prothrombin-time changes |
| Midazolam / lovastatin | No significant effect on exposure |
| Digoxin | No significant effect on steady-state pharmacokinetics in the cited study |
| Aspirin | Tadalafil did not potentiate aspirin-associated prolongation of bleeding time |
| Theophylline | No significant PK effect; small additional heart-rate increase observed, clinical significance unknown |
Current CIALIS labeling states that the safety and efficacy of combining CIALIS with other PDE5 inhibitors or other erectile-dysfunction treatments have not been studied. Patients are instructed not to take CIALIS with other PDE5 inhibitors, including ADCIRCA.
This is not the same interaction category as the formal nitrate or riociguat contraindications. The label's concern is that combination safety and efficacy have not been established rather than that all ED-treatment combinations share one proven interaction mechanism.
Comparing tadalafil with another ED medicine is therefore fundamentally different from combining the treatments.
| Combination | Current label position |
|---|---|
| CIALIS + another PDE5 inhibitor | Safety and efficacy not established; patients are instructed not to combine |
| CIALIS + ADCIRCA | Do not combine |
| Tadalafil + another ED treatment | Combination safety and efficacy have not been established |
Tadalafil has multiple clinically relevant interactions, but only a subset belong to the formal contraindication category. Organic nitrates and guanylate cyclase stimulators are prohibited combinations, whereas alpha-blockers, antihypertensives, alcohol and CYP3A4-modifying drugs have different label instructions.
Using 'contraindicated' for every interaction overstates some risks, while describing a contraindicated combination as merely a possible interaction understates others. Regulatory language is therefore part of accurate interaction interpretation.
The formal do-not-use framework is covered on the tadalafil contraindications page.
| Interaction | Correct high-level category |
|---|---|
| Organic nitrates | Contraindicated |
| Riociguat / GC stimulators | Contraindicated |
| Alpha-blockers | Caution / indication-specific not-recommended context |
| Antihypertensives | Additive blood-pressure interaction |
| Potent CYP3A4 inhibitors | Exposure interaction with regimen-specific restrictions |
| CYP3A4 inducers | Exposure-reducing interaction |
A tadalafil interaction review should extend beyond drugs obviously associated with erectile dysfunction. Cardiovascular medicines, antifungals, antivirals, antibiotics, antiseizure drugs, alcohol and some foods can affect one of the relevant pharmacodynamic or pharmacokinetic pathways.
Current CIALIS patient information advises patients to tell healthcare professionals about prescription and nonprescription medicines, vitamins and herbal supplements. This matters because a person may not recognize a medicine as a nitrate, alpha-blocker, CYP3A4 modifier or other interacting treatment from its brand name alone.
Medication changes can also alter a previously stable interaction context, so an established tadalafil regimen should not automatically be assumed to remain unchanged when another drug is started or stopped.
| Interaction review | Why it matters |
|---|---|
| Organic nitrate? | Formal contraindication |
| GC stimulator such as riociguat? | Formal contraindication |
| Alpha-blocker or antihypertensive? | Potential additive blood-pressure lowering |
| CYP3A4 inhibitor? | May increase tadalafil exposure |
| CYP3A4 inducer? | May decrease tadalafil exposure |
| Substantial alcohol intake? | Can amplify vasodilatory and orthostatic effects |
| Another PDE5 inhibitor or ED treatment? | Combination safety and efficacy may not be established |
Interaction lists are easy to misread when mechanism and regulatory language are removed. A drug that raises tadalafil exposure is not automatically contraindicated, and a drug that does not alter tadalafil concentration can still produce an important pharmacodynamic interaction.
The reverse is also true: a small laboratory or pharmacokinetic change is not automatically a clinically dangerous interaction. The antacid findings demonstrate why total exposure, absorption rate and clinical consequence need to be separated.
A useful interaction assessment therefore asks what changed, how strong the evidence is and what the current label actually instructs.
| Misinterpretation | Better interpretation |
|---|---|
| Every interacting drug is contraindicated | Only specific combinations are formally contraindicated |
| No change in tadalafil blood level means no interaction | Pharmacodynamic effects can still add together |
| Any PK change means a dangerous interaction | The affected parameter and clinical consequence matter |
| All CYP3A4 modifiers have the same effect size | Direction and magnitude depend on the specific modifier |
The major tadalafil interaction categories differ substantially in mechanism and severity. Organic nitrates and guanylate cyclase stimulators such as riociguat are formal contraindications, while alpha-blockers, antihypertensives and substantial alcohol intake are primarily important because of additive vasodilatory and blood-pressure effects.
CYP3A4 interactions work differently by changing tadalafil exposure. Inhibitors can increase exposure, whereas inducers can lower it and potentially reduce efficacy; quantitative PK effects and detailed regimen implications belong on the dedicated CYP3A4 page.
Not every co-administered substance produces a clinically important interaction. Current labeling includes examples of absorption changes without altered AUC and several controlled studies showing little or no meaningful tadalafil effect on other drug exposures, reinforcing that each interaction should be interpreted by mechanism, evidence and label category.
Major interaction categories in current U.S. labeling include organic nitrates, guanylate cyclase stimulators such as riociguat, alpha-blockers, antihypertensives, CYP3A4 inhibitors, CYP3A4 inducers and substantial alcohol consumption.
Organic nitrates and guanylate cyclase stimulators such as riociguat are contraindicated with tadalafil. Other interactions have different label instructions and should not automatically be classified as contraindications.
Routine concomitant use is contraindicated. Nitroglycerin is an organic nitrate, and tadalafil can potentiate nitrate-induced hypotension.
No. Current U.S. labeling contraindicates tadalafil with guanylate cyclase stimulators such as riociguat because their hypotensive effects can be potentiated.
Alpha-blockers are not a blanket tadalafil contraindication, but the combination can cause additive blood-pressure lowering. Current labeling uses a caution framework for ED and states that tadalafil plus an alpha-blocker is not recommended for treatment of BPH.
Tadalafil can augment the blood-pressure-lowering effect of antihypertensive medicines. Current labeling does not classify routine antihypertensive use as a blanket contraindication, but the medication and blood-pressure context still matter.
Yes. Both tadalafil and alcohol have vasodilatory effects. Current labeling warns that substantial alcohol intake, using approximately 5 units or more as an example, can increase orthostatic symptoms such as dizziness and reduced standing blood pressure.
Not in the cited CIALIS interaction studies. Alcohol did not alter tadalafil plasma concentrations and tadalafil did not alter alcohol plasma concentrations; the important interaction is primarily pharmacodynamic.
Tadalafil is metabolized predominantly by CYP3A4. Inhibiting this pathway can reduce tadalafil metabolism and increase systemic exposure.
Current CIALIS labeling states that grapefruit juice would likely increase tadalafil exposure through CYP3A4 inhibition. The magnitude should not be assumed to be identical to directly studied inhibitors such as ketoconazole.
CYP3A4 inducers can reduce tadalafil exposure. Rifampin is the main studied example, while drugs such as carbamazepine, phenytoin and phenobarbital are expected to have the same direction of effect.
A magnesium hydroxide/aluminum hydroxide antacid reduced the apparent rate of tadalafil absorption in the cited study but did not change total tadalafil exposure measured by AUC.
In controlled studies, tadalafil did not significantly affect S-warfarin or R-warfarin exposure and did not alter the prothrombin-time changes produced by warfarin.
In the study described in current CIALIS labeling, tadalafil did not potentiate the increase in bleeding time caused by aspirin.
Current labeling reports no significant effect of tadalafil on steady-state digoxin pharmacokinetics in the cited healthy-subject study.
Current CIALIS labeling states that the safety and efficacy of combining CIALIS with other PDE5 inhibitors or other ED treatments have not been studied and instructs patients not to take CIALIS with other PDE5 inhibitors.
Once-daily tadalafil produces continuous plasma exposure. Current labeling therefore emphasizes considering ongoing interactions with nitrates, alpha-blockers, antihypertensives, potent CYP3A4 inhibitors and substantial alcohol consumption.
No. Some combinations are contraindicated, some can add to blood-pressure lowering, some change tadalafil exposure and others produce little or no clinically important pharmacokinetic effect in controlled studies. The mechanism and current label wording determine how the interaction should be interpreted.