CIALIS for daily use remains in your body for as long as you take it. Tell your doctor about all medications, especially if you take nitrates (often used for chest pain) or medicines for blood pressure, alpha blockers, antifungals, or HIV, so your doctor can be aware of potential drug interactions. Don't drink alcohol in excess (to a level of intoxication) with CIALIS, as this may increase your chances of getting dizzy or lowering your blood pressure. CIALIS does not protect against sexually transmitted diseases, including HIV. The most common side effects with CIALIS were headache and upset stomach. Backache and muscle ache were also reported, sometimes with delayed onset. As with any ED tablet, in the rare event of an erection lasting more than 4 hours, seek immediate medical help to avoid long-term injury. In rare instances, men taking prescription ED tablets (including CIALIS) reported a sudden decrease or loss of vision or hearing (sometimes with ringing in the ears and dizziness). It's not possible to determine if these events are related directly to the ED tablets or to other factors. If you have a sudden decrease or loss of vision or hearing, stop taking any ED tablet, including CIALIS and call your doctor right away. Take one Cialis tablet by mouth before sexual activity. In some patients, the ability to have sexual activity was improved at 30 minutes after taking Cialis. The ability to have sexual activity was improved up to 36 hours after taking Cialis. You and your doctor should consider this in deciding when you should take Cialis prior to sexual activity. Some form of sexual stimulation is needed for an erection to happen. Cialis may be taken with or without meals.