Hull midfielder Jake Livermore faces a possible two-year ban after testing positive for cocaine, while Sheffield United and Wolves also suspended players last week.
“They probably do not appreciate the consequences, not just for them and their careers, but for their families,” said PFA chief executive Gordon Taylor. “The education and regulations need to be enhanced.”
Livermore, who has one England cap and joined Hull from Tottenham for £8m last summer, is believed to have tested positive after a match – a detail that would leave him facing tougher punishment.
Football Association rules stipulate that players who fail post-match tests for recreational drugs can be banned for up to two years, while those who do so at other times risk six-month suspensions.
Hull manager Steve Bruce, whose side must beat Manchester United in their final match on Sunday to avoid relegation from the Premier League, said he was “shocked, saddened, disappointed and angry”.
Sheffield United forward Jose Baxter and Wolves goalkeeper Aaron McCarey have also been suspended by their clubs following failed tests. Both players have denied wrongdoing.