Many high profile, household football names, including Diego Maradona, Romario, Frank de Boer, Marco Boriello, Paddy Kenny, Stan Lazaridis, Edgar Davids, Christophe Dugarry, Fernando Couto, Jaap Stam, Quim and Josep Guardiola have been caught out taking performance enhancing drugs. What is most concerning is that many footballers, including Guardiola, Couto, Stam, de Boer and Davids, have been caught using nandrolone, a substance that assists in muscle growth, red cell production and bone density, thus, either bulking up or recovering from injury can be made far easier. Several studies have been undertaken in this field, one of these (link) has some rather alarming conclusions:
Many players use supplements, although almost one in five players does so without seeking qualified professional advice from anyone within the club. Blood tests are rarely used to monitor the health of players. One third of players had not been tested for drugs within the preceding two years, and 60% felt that they were unlikely to be tested in the next year.
And then there's Juventus 1994-98, whose doctor was sentenced to 22 months in prison for administering EPO to the players, a very real example that systematic, team-wide doping does exist in professional football:
Some sports, such as cycling, have taken the right step forward in dealing with this issue with frequent drug testing but others like football lag far behind. Tennis is another example. Rafael Nadal recently withdrew from the Olympics, citing a dodgy knee, but its more likely he withdrew as he would not be offered the protection that the ITF offers him in the Olympic Games, where drug tests are administered by WADA. While that may sound conspiratorial, consider this:
The UCI (cycling's governing body) administered 13,745 drug tests in 2012. In 2009, the ITF (tennis' governing body) administered 2126.
Here is a brief history of doping in sport up until the year 2003: