The text on YouTube that accompanies this advert explains the background to this ad very well:
"This is an advert from Pfizer in response to research which found one in 10 men in the UK purchase prescription-only medicines from unregulated sources such as internet sites, every year. It is estimated that between 50-90 per cent of medicines sold in this way have proven to be counterfeit which means they are taking a real gamble with health."
As always, there is an accompanying website, www.realdanger.co.uk, that gives you a lot more information about the dangers involved and an email address where you can report counterfeit medication.
WARNING: Do not watch the following if you have just eaten, are currently eating, or are about to eat!
Get Real, Get a Prescription - Pfizer "Real Danger" Advert