A thoughtful Fernando Alonso. ANSA/Daniel Dal Zennaro
Nothing new
The governing body of F1, the FIA, became a signatory to the WADA Code in December 2010, following which drivers, including Narain Karthikeyan, have been tracked down and tested for banned substances.
The FIA itself had set up its own anti-doping regulations in January 2006, which led to Nico Rosberg being tracked down and tested while on holiday in 2009.
Doping in motorsport is extremely rare and barely heard of with the exception of cases like Grand Prix motorcycle racer Anthony West, who tested positive for the stimulant methylhexaneamine in late October last year.
Tweet times
Alonso and Ricciardo both took to the microblogging site Twitter to share the news of their surprise visitors. "Got drug tested early hours this morning," Ricciardo tweeted. "All of a sudden p*****g in your own home becomes difficult with someone staring over your shoulder."
No F1 driver who has been tested is yet to test positive for any of the substances on WADA's list of contraband items.
However, veteran F1 observers have not ruled out the common use of recreational drugs by drivers between races and during the off-season.