Mounjaro and Tadalafil Interaction: What Patients and Clinicians Need to Know

Is There a Direct Interaction Between Mounjaro and Tadalafil?

The Mounjaro label's drug interactions section covers insulin secretagogues or insulin, and oral medicines affected by delayed gastric emptying; it does not list tadalafil [1]. The Cialis label, which covers tadalafil tablets for erectile dysfunction and benign prostatic hyperplasia, does not list tirzepatide [2]. Mounjaro is approved for type 2 diabetes in adults and children 10 years and older, and for reducing cardiovascular risk in adults with type 2 diabetes at high risk; it is not labeled for weight loss [1].

The two labels point to different effects that could overlap. Tadalafil is a PDE5 inhibitor with mild systemic vasodilatory properties that can cause transient blood pressure decreases [2]. The Cialis label names alpha-blockers, antihypertensives and substantial alcohol as situations where hypotension can occur [2]. The Mounjaro label warns that acute kidney injury from volume depletion has occurred, mostly after nausea, vomiting or diarrhea led to dehydration [1]. The effect of using the two drugs together has not been measured.

What Does Tadalafil Do to Blood Pressure?

In a clinical pharmacology study, tadalafil 20 mg produced a mean maximal decrease in supine blood pressure, relative to placebo, of 1.6/0.8 mm Hg in healthy subjects [2]. The Cialis label also warns that use with alpha-blockers, antihypertensives or substantial alcohol may lead to hypotension [2].

With alpha-blockers the label is specific. For ED, the label says to be stable on the alpha-blocker first and to start tadalafil at the lowest dose [2]. For BPH, the label does not recommend combining tadalafil with an alpha-blocker because efficacy has not been adequately studied and blood pressure can fall [2]. In healthy volunteers, tadalafil 20 mg with doxazosin 8 mg/day gave a placebo-subtracted maximal standing systolic fall of 9.8 mm Hg; with tamsulosin 0.4 mg the standing fall was 1.7 mm Hg with tadalafil 10 mg and 2.3 mm Hg with 20 mg [2].

What Does Tirzepatide Do That Matters Here?

Mounjaro's common adverse reactions are gastrointestinal. In the Mounjaro label pool of two placebo-controlled trials in adults with type 2 diabetes, nausea occurred in 12%, 15% and 18% on 5, 10 and 15 mg versus 4% on placebo; diarrhea in 12%, 13% and 17% versus 9%; vomiting in 5%, 5% and 9% versus 2% [1]. The label says acute kidney injury due to volume depletion has been reported, and that renal function should be monitored in patients reporting adverse reactions that could lead to volume depletion, especially during dose initiation and escalation [1].

The label also says tirzepatide delays gastric emptying and has the potential to affect absorption of oral medicines [1]. Tadalafil is an oral medicine, but that warning is general and does not name tadalafil [1]. Tadalafil's absorption is not influenced by food, and its median peak concentration occurs about 2 hours after a dose [2].

Is There a Pharmacokinetic Interaction?

Tadalafil is a substrate of and predominantly metabolized by CYP3A4 [2]. Tirzepatide is not metabolized by CYP enzymes and has low in vitro potential to inhibit or induce CYP enzymes [1]. The Mounjaro label's oral-medicine warning is about delayed gastric emptying, not CYP3A4 [1].

Tadalafil's own label shows how much CYP3A4 changes its exposure: ketoconazole 400 mg daily raised tadalafil 20 mg AUC by 312%, and rifampin 600 mg daily cut tadalafil 10 mg AUC by 88% [2]. The Cialis label's CYP3A4 interaction section does not list tirzepatide [2].

What About Nitrates and Alcohol?

Nitrates are contraindicated with tadalafil. The Cialis label contraindicates any form of organic nitrate, used regularly or intermittently, because tadalafil potentiates the hypotensive effect. It also contraindicates guanylate cyclase stimulators such as riociguat, and use in people with known serious hypersensitivity to tadalafil [2]. For a life-threatening situation in which a nitrate is medically necessary, the label says at least 48 hours should have elapsed after the last Cialis dose before a nitrate is considered, and then only under close medical supervision with hemodynamic monitoring [2]. That is an emergency rule, not permission to combine them. In a 150-man crossover study, standing blood pressure fell below the threshold more often on tadalafil after nitroglycerin at 4, 8 and 24 hours, with no difference at 48, 72 and 96 hours [3]. The Mounjaro label's contraindications are a personal or family history of medullary thyroid carcinoma or MEN 2 and serious hypersensitivity to tirzepatide or an excipient; nitrates are not on that list [1].

Alcohol: The Cialis label says both alcohol and tadalafil are mild vasodilators. Substantial alcohol, 5 units or more, with Cialis can increase orthostatic signs and symptoms, including higher heart rate, lower standing blood pressure, dizziness and headache [2]. Tadalafil did not change alcohol levels and alcohol did not change tadalafil levels [2].

What Else Is Relevant to Each Drug's Label?

The Cialis label says treatments for erectile dysfunction, including Cialis, should not be used in men for whom sexual activity is inadvisable because of cardiovascular status [2]. It lists cardiovascular conditions that were not included in clinical trials and for which Cialis is not recommended: myocardial infarction within 90 days, unstable angina or angina during intercourse, NYHA class 2 or greater heart failure within 6 months, uncontrolled arrhythmia, blood pressure below 90/50 mm Hg, uncontrolled hypertension, and stroke within 6 months [2].

Kidney function changes tadalafil dosing. The Cialis label limits as-needed tadalafil to 5 mg no more often than every 72 hours when creatinine clearance is below 30 mL/min or the person is on hemodialysis, and once-daily use is not recommended in that group [2]. Neither label specifies a dose change for using the two drugs together [1][2].