People can increase their chances of receiving a free sample of Viagra by mail by being proactive and remaining informed. The titration studies, in which most patients received mg, showed similar results. The Food and Drug Administration recommends taking Viagra around one hour before you intend on having sex. Occasionally patients may be asked to monitor their blood pressure and pulse after being newly prescribed sildenafil, after an increase in dosage, or after the addition of CYP3A4 inhibitors. Patients are advised not to exceed a maximum dosing frequency of once daily. Fact Checker: Daniel Boyer M. You can test a medication using a sample to see if any side effects are tolerable and if the advantages outweigh the risks.Viagra is absorbed quickly into your body. It can start working within 30 minutes, but it may take a couple hours for some people. However, one study on Viagra found that about 70% of men achieved erections in 30 minutes, and more than 80% of men achieved erections within 45 minutes. For most men, the effects of Viagra will start within .  · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose. Consumer Reports Best Buy Drugs shares how you might be able to get generic Viagra, known as sildenafil, at a much lower price.