Critical Drug Interactions with Sildenafil
Dangerous Interactions - Never Combine
The most serious drug interaction with British Viagra occurs with nitrate medications. Combining sildenafil with nitrates such as glyceryl trinitrate (GTN spray), isosorbide mononitrate, or isosorbide dinitrate can cause a severe, potentially fatal drop in blood pressure. This interaction remains dangerous for 24 hours after taking sildenafil, so nitrates must not be used during this period.
Riociguat, used for pulmonary arterial hypertension, is another medication that must never be combined with Viagra or generic sildenafil due to similar dangerous blood pressure effects.
Blood Pressure Medications
Many blood pressure medications can interact with sildenafil, though not necessarily dangerously. Alpha-blockers like doxazosin, tamsulosin, and alfuzosin require particular caution. When starting sildenafil treatment, patients taking alpha-blockers should begin with the lowest dose (25mg) and ensure their alpha-blocker therapy is stable.
Other antihypertensive medications including ACE inhibitors, calcium channel blockers, and diuretics may enhance the blood pressure-lowering effects of sildenafil. While not contraindicated, patients may experience dizziness or lightheadedness, particularly when standing up quickly.
Medications Affecting Sildenafil Levels
Certain medications can alter how quickly your body processes sildenafil, affecting its strength and duration. Ketoconazole, itraconazole, and other antifungal medications can increase sildenafil levels, potentially requiring dose reduction. Similarly, HIV protease inhibitors like ritonavir significantly increase sildenafil concentrations.
Conversely, medications that speed up liver metabolism, such as rifampicin or certain epilepsy medications, may reduce sildenafil effectiveness. Your prescriber will consider these interactions when determining appropriate dosing.
Other Important Interactions
Recreational drugs, particularly 'poppers' containing amyl nitrite or butyl nitrite, pose the same dangerous risks as medical nitrates and must be avoided. Excessive alcohol consumption can increase the risk of side effects and may reduce the effectiveness of treatment.
Grapefruit juice may slightly increase sildenafil levels, though this interaction is generally not clinically significant. However, it's advisable to maintain consistent grapefruit consumption patterns if you regularly consume it.
EverydayMeds Clinical Assessment
At EverydayMeds, our UK-licensed prescribers conduct thorough medication reviews during the consultation process. Whether you choose branded Viagra or generic sildenafil, we ensure all potential interactions are identified and managed appropriately. Our clinical team provides clear guidance on timing medications and managing any necessary adjustments to your treatment regimen.
