Viagra & Cialis With Ozempic, Wegovy, Zepbound: Drug Interaction Evidence Review

Sildenafil (Viagra), tadalafil (Cialis), and avanafil (Stendra) are PDE-5 inhibitors metabolized primarily through hepatic cytochrome P450 3A4. GLP-1 receptor agonists — semaglutide (Wegovy, Ozempic), tirzepatide (Zepbound, Mounjaro), liraglutide (Saxenda, Victoza), and oral semaglutide (Rybelsus) — are peptide drugs cleared by general proteolysis. The two drug classes share no overlapping metabolic pathway. There is no known clinically significant pharmacokinetic interaction. The FDA prescribing information for Wegovy, Ozempic, Zepbound, Mounjaro, Saxenda, and Rybelsus does not list PDE-5 inhibitors in the Drug Interactions section. The FDA labels for Viagra, Cialis, Levitra, and Stendra do not list GLP-1 receptor agonists. The one consideration worth flagging is a theoretical additive blood-pressure effect: GLP-1 medications lower systolic blood pressure by roughly 3–6 mmHg in non-diabetic adults (Kennedy 2023 meta-analysis^[9]); PDE-5 inhibitors also produce a small vasodilator effect of similar magnitude (Webb 1999^[4]). The additive effect is generally well-tolerated but warrants attention in patients already on antihypertensive therapy or prone to postural hypotension. The drug-interaction-checker verdict is green. This article walks the verified evidence and flags the few practical caveats clinicians actually monitor.

The honest summary

• No pharmacokinetic interaction. Sildenafil, tadalafil, and avanafil are CYP3A4 substrates. Semaglutide, tirzepatide, and liraglutide are peptides cleared by proteolysis. The pathways don't overlap.
• Neither drug label flags the other. The FDA prescribing information for the major GLP-1 brands (Wegovy, Ozempic, Zepbound, Mounjaro, Saxenda, Rybelsus) does not list PDE-5 inhibitors in Section 7 (Drug Interactions). The Viagra, Cialis, Levitra, and Stendra labels do not list GLP-1 receptor agonists.
• Theoretical additive vasodilation. GLP-1s drop systolic blood pressure ~3–6 mmHg (Kennedy 2023 meta-analysis^[9], SELECT trial^[10]). Sildenafil drops systolic ~8 mmHg acutely (Webb 1999^[4]). Stacked effects can produce mild postural symptoms in susceptible patients.
• The hard contraindication is nitrates with any PDE-5i (Webb 2000 JACC^[5]) — not GLP-1s. This is the same rule that has held since 1998 regardless of weight-loss medication status.
• GI side-effect overlap. Dyspepsia is a listed side effect of PDE-5 inhibitors. Nausea, dyspepsia, and reflux are listed side effects of GLP-1s (Wharton 2022 clinical practice recommendations^[6]). The symptoms can compound; the underlying mechanism does not.
• Same-day dosing is fine. No time-of-day conflict between weekly or daily GLP-1 injections, oral semaglutide (Rybelsus), oral orforglipron (Foundayo), or on-demand sildenafil or daily tadalafil 2.5–5 mg.

Mechanism question: why these two classes don't interact

Pharmacokinetic drug interactions usually happen at one of three points: a shared cytochrome P450 metabolizing enzyme (most commonly CYP3A4, CYP2D6, CYP2C9, or CYP2C19), a shared transporter (P-glycoprotein, OATP1B1), or competition at the same plasma protein binding site. PDE-5 inhibitors and GLP-1 agonists share none of these.

Sildenafil, tadalafil, and avanafil are small molecules. The Goldstein 1998 NEJM pivotal trial of sildenafil (Sildenafil Study Group^[1]) and the Brock 2002 J Urol integrated tadalafil analyses^[2] established the clinical efficacy of the class. Pharmacokinetically all three are absorbed orally, distributed via plasma protein binding, and metabolized primarily by hepatic CYP3A4 with a minor CYP2C9 contribution. Clinically meaningful PDE-5i drug interactions are with strong CYP3A4 inhibitors (ketoconazole, ritonavir, clarithromycin — which raise PDE-5i plasma levels) and strong CYP3A4 inducers (rifampin, carbamazepine, chronic St John's wort — which lower them).

Semaglutide, tirzepatide, liraglutide, and exenatideare peptides — chains of amino acids 30–40 residues long. They are not CYP3A4 substrates. They are not metabolized by any cytochrome P450 enzyme. They are cleared by general proteolysis (ubiquitous peptidases that exist throughout the body) followed by renal elimination of small peptide fragments. The Wegovy, Ozempic, Zepbound, Mounjaro, Saxenda, Victoza, and Rybelsus labels all state explicitly that cytochrome P450-mediated drug interactions are not expected with the peptide itself.

Oral semaglutide (Rybelsus) and oral orforglipron (Foundayo) are the two exceptions worth understanding. Rybelsus is absorbed in the stomach using the salcaprozate sodium (SNAC) absorption enhancer, which means co-ingestion with food or large volumes of fluid lowers absorption — but the co-ingestion effect is with the absorption-enhancer chemistry, not with the metabolic pathway of any second drug. Orforglipron is a small molecule and is hepatically metabolized through CYP3A4 in part, which makes it the one GLP-1-class product where strong CYP3A4 inhibitors or inducers could theoretically matter. Sildenafil and tadalafil are CYP3A4 substrates, not inhibitors or inducers, so there is no meaningful effect in the other direction either.

What the FDA labels actually say

The drug-interaction sections (Section 7) of the major relevant labels, summarized verbatim from the DailyMed-hosted current prescribing information:

• Wegovy (semaglutide 2.4 mg): Section 7 covers oral medications (Rybelsus self-reference; delayed gastric emptying may impact absorption of concomitantly administered oral medications). No PDE-5i mention.
• Ozempic (semaglutide 0.5/1/2 mg): Same as Wegovy. Section 7 is brief: delayed gastric emptying and oral medication absorption. No PDE-5i mention.
• Zepbound (tirzepatide): Section 7 flags delayed gastric emptying with potential impact on oral contraceptive absorption (the recommendation is to add a non-oral contraceptive or barrier method for 4 weeks after initiation and after each dose escalation). No PDE-5i mention.
• Mounjaro (tirzepatide): Same as Zepbound.
• Saxenda (liraglutide 3 mg): Section 7 covers delayed gastric emptying and warfarin INR monitoring. No PDE-5i mention.
• Rybelsus (oral semaglutide): Section 7 covers the levothyroxine absorption interaction (concomitant dosing increases T4 exposure) and a general oral-medication absorption note. No PDE-5i mention.
• Viagra (sildenafil): Section 7 covers nitrates (absolute contraindication), alpha-blockers (symptomatic hypotension warning), CYP3A4 inhibitors and inducers, ritonavir (50% dose reduction), and amlodipine (small additive BP reduction). No GLP-1 mention.
• Cialis (tadalafil): Section 7 covers nitrates (absolute contraindication), alpha-blockers, CYP3A4 inhibitors and inducers, and alcohol (potential orthostatic hypotension). No GLP-1 mention.
• Stendra (avanafil): Section 7 covers nitrates (absolute contraindication), alpha-blockers, CYP3A4 inhibitors, and alcohol. No GLP-1 mention.

The absence of a drug-interaction listing in both directions is the strongest negative evidence available. Both classes have been on the market long enough (PDE-5 inhibitors since 1998, GLP-1 receptor agonists since 2005, semaglutide since 2017, tirzepatide since 2022) for a clinically significant interaction signal to have emerged in post-marketing surveillance if it existed.

The blood-pressure question

Both drug classes lower blood pressure modestly. The clinical question is whether the combined effect is meaningful in practice.

GLP-1 receptor agonists. The Kennedy 2023 systematic review and meta-analysis^[9] pooled semaglutide trials in non-diabetic adults with overweight or obesity and reported a mean reduction in systolic blood pressure of approximately 4.8 mmHg and diastolic ~2.5 mmHg. The Wilding 2021 STEP-1 NEJM trial^[7] reported systolic BP -6.2 mmHg vs placebo at 68 weeks on semaglutide 2.4 mg. The Jastreboff 2022 SURMOUNT-1 NEJM trial^[8]on tirzepatide 15 mg reported systolic BP reductions of roughly 6–7 mmHg. The Lincoff 2023 SELECT NEJM cardiovascular outcomes trial^[10] in 17,604 non-diabetic adults with established cardiovascular disease confirmed similar BP reductions over a median 39.8 months of treatment.

PDE-5 inhibitors. The Webb 1999 Am J Cardiol drug-interaction studies^[4] measured sildenafil 100 mg co-administered with the calcium-channel blocker amlodipine in hypertensive patients. The additive systolic BP reduction was approximately 8 mmHg above the amlodipine effect alone. The Webb 2000 JACC paper^[5] measured sildenafil + nitric-oxide donor drugs (sublingual nitroglycerin) in patients with stable angina and documented profound, clinically dangerous hypotension — the basis for the absolute contraindication between PDE-5 inhibitors and nitrates that has held since 1998. Tadalafil and avanafil produce similar acute BP reductions in the 5–10 mmHg systolic range; the magnitude is slightly smaller for tadalafil because of its longer half-life and flatter peak.

How sildenafil and tadalafil compare to GLP-1 BP effects

The practical interpretation: a patient on weekly semaglutide 2.4 mg who takes sildenafil 100 mg on a Saturday evening will see a transient additional 5–8 mmHg systolic reduction during the 4–6 hour window after PDE-5i dosing, on top of the sustained GLP-1-mediated ~6 mmHg baseline reduction. For most adults this is well-tolerated and produces no symptoms. The patients in whom it matters are those who are also taking antihypertensive therapy (especially multiple agents), those already prone to orthostatic hypotension, and those who are also volume-depleted from GLP-1-related reduced fluid intake (a common downstream of nausea and reduced appetite, Wharton 2022^[6]).

Postural hypotension monitoring

The practical advice clinicians give when a patient on a GLP-1 adds an as-needed PDE-5 inhibitor for the first time:

• First dose at home, not in a hotel. Take the first PDE-5i dose in a familiar setting with someone who can intervene if symptoms occur. Stand up slowly for the first 4–6 hours after dosing.
• Avoid alcohol during the first trial.Alcohol is an independent vasodilator and is listed as a potential orthostatic-hypotension contributor on the Cialis and Stendra labels.
• Hydrate adequately. Volume depletion from GLP-1-related reduced fluid intake amplifies the symptomatic hypotension risk. The Wharton 2022 GI side-effect guidance^[6] emphasizes hydration regardless of the PDE-5i question.
• Lower starting dose if on multiple antihypertensives. The Viagra label recommends starting sildenafil at 25 mg (vs the standard 50 mg) in patients on an alpha-blocker or multiple antihypertensives. The same prudence applies for a patient on a GLP-1 plus two or more BP medications, even though the label does not mandate it.
• Daily low-dose tadalafil is the smoother option. Tadalafil 2.5–5 mg taken daily produces a small, sustained PDE-5i effect rather than an acute peak, which is generally better tolerated in patients who get orthostatic symptoms on as-needed dosing.

The dyspepsia and GI overlap

Dyspepsia (upper-abdominal discomfort, reflux-type symptoms) is a listed adverse reaction on the Viagra, Cialis, and Stendra labels — it is one of the more common reasons patients discontinue PDE-5 inhibitors. The mechanism is cross-reactivity with PDE-5 in the lower esophageal sphincter, which relaxes and produces reflux-type symptoms in susceptible individuals.

Nausea, dyspepsia, reflux, vomiting, and constipation are listed adverse reactions on the Wegovy, Ozempic, Zepbound, Mounjaro, Saxenda, and Rybelsus labels — the GI side effects are dose-related and most prominent during dose escalation. The Wharton 2022 clinical practice recommendations^[6] document the prevalence and provide the evidence-based management approach (small portions, slow eating, low-fat meals, antiemetics when appropriate).

The two side-effect profiles can compound symptomatically. A patient already coping with mid-titration GLP-1 nausea who adds sildenafil 100 mg before dinner may experience a worse reflux episode that evening than they would on either drug alone. This is not a pharmacokinetic interaction; it is additive end-organ side effects in the same anatomical region. Practical workarounds: take the PDE-5i 1–2 hours after a small meal rather than immediately before a large one; consider tadalafil daily 2.5–5 mg (lower peak symptom burden) rather than sildenafil on-demand; defer the first PDE-5i trial until the GLP-1 titration plateau is reached.

Pulmonary arterial hypertension dosing

Sildenafil is also FDA-approved for pulmonary arterial hypertension under the brand name Revatio(20 mg three times daily). Tadalafil is FDA-approved for the same indication under the brand name Adcirca(40 mg daily). At the PAH doses, sildenafil exposure is lower per dose than the 50–100 mg ED dose, but cumulative daily exposure is meaningful and the chronic vasodilator effect is therapeutic.

The same interaction logic applies. There is no pharmacokinetic interaction between PAH-dose sildenafil or tadalafil and GLP-1 receptor agonists. The blood-pressure consideration is in principle the same — small additive vasodilation — but PAH patients are typically managed by a specialty pulmonology team that is already titrating multiple vasoactive medications and monitoring closely. The relevant clinical decisions on these patients are not made from a primary-care PDE-5i + GLP-1 perspective; they are made from the PAH treatment plan, and adding a GLP-1 for weight-loss indications should be coordinated with the pulmonology team.

Avanafil + GLP-1

Avanafil (Stendra) is the newest PDE-5 inhibitor in the US market (approved 2012, Goldstein 2012 J Sex Med pivotal RCT^[3]). It has the most selective PDE-5 affinity of the four available agents (sildenafil, tadalafil, vardenafil, avanafil) and the fastest onset (~15 min). It is also a CYP3A4 substrate. The same logic that applies to sildenafil and tadalafil applies: no pharmacokinetic interaction with GLP-1 receptor agonists, theoretical additive vasodilation with the same magnitude as sildenafil. The Stendra label does not list GLP-1 receptor agonists in Section 7.

Drug-interaction-checker verdict

On the commercial drug-interaction checkers (Lexicomp, Micromedex, Drugs.com, Epocrates), the combination of sildenafil, tadalafil, or avanafil with semaglutide, tirzepatide, liraglutide, or oral semaglutide returns no documented interaction. The verdict is green at the database level. The checkers will flag, as they should, the unrelated PDE-5i contraindications (nitrates, strong CYP3A4 inhibitors, alpha-blocker timing) and the unrelated GLP-1 considerations (oral medication absorption, hormonal contraception escalation window on tirzepatide).

The absence of a documented interaction is not the same as an absence of any consideration. The two clinical caveats are the ones already noted: (1) the small additive systolic BP effect, which matters in patients on multiple antihypertensives or prone to orthostasis; and (2) the overlapping GI side-effect burden, which is additive symptomatically without being a true drug interaction. Neither is a contraindication. Both are worth a 2-minute conversation at the first prescription.

Dose timing

There is no time-of-day or day-of-week conflict between any GLP-1 regimen and any PDE-5i regimen:

• Weekly injectable GLP-1 (Wegovy, Ozempic, Zepbound, Mounjaro) administered any day of the week: PDE-5i taken on any other day or the same day is fine.
• Daily injectable GLP-1 (Saxenda, Victoza): morning or evening dosing is per patient preference; PDE-5i on demand or daily is fine concurrently.
• Rybelsus (oral semaglutide): taken on an empty stomach in the morning with no more than 4 oz water, then a 30-minute wait before food, drink, or other oral medication. A PDE-5i can be taken later in the day with no interaction.
• Foundayo (oral orforglipron): taken once daily without food restrictions in the pivotal trial program. PDE-5i timing is independent.
• Sildenafil or avanafil on-demand: 30–60 min before sexual activity; the GLP-1 schedule is unaffected.
• Tadalafil on-demand 10–20 mg or daily 2.5–5 mg: any GLP-1 regimen is compatible.

What this article does not say

• It does not say that the GLP-1 itself improves erectile function. The weight-loss-mediated improvement in erectile function in men with obesity is well-documented across the weight-loss literature, but this is a downstream effect of weight loss + improved metabolic health, not a direct mechanism of the GLP-1 medication. The honest framing is that successful weight loss of 10–15% body weight, regardless of how it is achieved, is associated with improved erectile function in observational and small RCT data — not that the medication is itself an ED treatment.
• It does not establish that PDE-5 inhibitors are safe in every individual on a GLP-1. The standard PDE-5i contraindications still apply (nitrate use, unstable angina, recent stroke or MI, severe hepatic impairment, severe hypotension, retinitis pigmentosa).
• It does not address vardenafil (Levitra/Staxyn) explicitly. The same class logic applies; the brand is less commonly prescribed in the US currently. No GLP-1 interaction is listed on the vardenafil label.
• It is not a substitute for clinical judgment. A patient starting both medications concurrently for the first time should have a conversation with the prescribing clinician about cumulative blood-pressure load and any underlying cardiovascular condition.

Bottom line

• There is no clinically significant pharmacokinetic interaction between sildenafil, tadalafil, or avanafil and any GLP-1 receptor agonist (semaglutide, tirzepatide, liraglutide, oral semaglutide, orforglipron).
• The FDA labels do not flag each other in either direction.
• The theoretical concern is a small additive systolic BP reduction of 5–10 mmHg, which is well-tolerated in most adults but worth attention in patients on multiple antihypertensives or prone to orthostasis.
• Dyspepsia and GI side effects can compound symptomatically — this is additive end-organ effect, not a drug interaction.
• The hard absolute contraindication remains PDE-5i + nitrates (Webb 2000^[5]), which is independent of GLP-1 status.
• Dose-timing is fully flexible. Same-day dosing is fine.
• Patients should still have the routine first-dose conversation with the prescribing clinician, particularly if on multiple antihypertensives.

Related research and tools

• Foundayo vs Wegovy vs Zepbound — the FDA-approved weight-loss interventions and how they compare on efficacy and side effects
• GLP-1 side-effect questions answered — the broader Q&A hub on Wegovy, Zepbound, Ozempic, and Mounjaro side effects
• Semaglutide overview — the Wegovy / Ozempic / Rybelsus drug-class page
• Tirzepatide overview — the Zepbound / Mounjaro drug-class page
• GLP-1 side-effect timeline tool — what to expect at each titration step

Important disclaimer. This article is educational and does not constitute medical advice. Patients on nitrates of any form (sublingual, oral, topical, IV) must not take a PDE-5 inhibitor under any circumstance; the nitrate + PDE-5i combination can produce life-threatening hypotension and is an absolute contraindication (Webb 2000 JACC). Patients with unstable cardiovascular disease, recent stroke or myocardial infarction, severe hepatic impairment, or severe baseline hypotension should discuss PDE-5 inhibitor use with their prescribing clinician before any dose. Patients on a GLP-1 receptor agonist who are also taking multiple antihypertensive medications should consider a lower starting PDE-5i dose and monitor for orthostatic symptoms during the first dose. PMIDs were independently verified against the PubMed E-utilities API on 2026-05-28; FDA prescribing-information summaries reflect current DailyMed-hosted labels at time of writing.

Last verified: 2026-05-28. Next review: every 12 months, or sooner if either FDA label updates its drug-interaction section, or new pharmacokinetic data on the combination is published.