Do not take more or less of it or take it more often than prescribed by your doctor. You can buy it from a store-based pharmacy or reputable online pharmacy with a prescription. This rare condition is more likely to occur if you have heart disease, high blood pressure, High Cholesterol, Diabetes, or eye problems, are more than 50 years old, or if you smoke. This increase in blood flow results in a firmer, longer-lasting erection. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure.CIALIS VIAGRA. Toll Free Phone: Toll Free Fax: Canada Pharmacy online has the best selection and discount prices on prescription and over-the-counter drugs. Everything you would expect from the largest online Canadian Pharmacy! Can You Buy Viagra Without a Prescription? Recent Blog Posts. Why Is . Viagra Dosage and Use Tips for First-Timers. Viagra dosage for erectile dysfunction (ED) is usually milligrams (mg), but those over 65 may start at 25 mg. Your doctor will also need to.  · You can take the drug 30 minutes to 4 hours before you anticipate sexual activity. Based on how well you respond to this dosage and any side effects you have, your doctor may either increase your.