http://candacenkoth.com/?q=number-of-retail-pharmacies-in-canada Search Engine Marketing refers to paid advertising. The amounts paid to advertise on Google and other search engines form the major crux of SEM. There are various types of ads/campaigns which are available like,

viagra on line – PPC – Pay per click

nhs prescription viagra cost – CPC – Cost per click

– CPM – Cost per impression

Depending upon the ultimate goals and needs of the client, the strategy is devised in combination of above campaign types to meet the desired results.

The most popular platform is ofcourse is Google followed by Bing & Yahoo.