Williams, part of Wales' all-conquering team in the 1970s, is among a clutch of internationals, including England's Jonathan Webb and Jeff Probyn, who have voiced concerns about drugs and their sport.
"Taking banned substances is fairly rife, and most of it is done in the off-season," Williams said.
"It is fairly well recognised that certain players have been on anabolic steroids and haven't been tested.
"I know of two players in Wales who are still playing, and have played at international level. I have had it confirmed by the two players," he claimed.
Williams, the fourth most capped player with 55 times appearances for his country, heard mixed reactions from the Welsh Rugby Union.
"JPR's accusations are obviously serious ones, and it does seem strange that he has not voiced his concern directly to the Union," said a WRU spokesman.
"The innuendo leaves an unsatisfactory feel about it, and it is now down to the Union to follow through what has been alleged and to ascertain what substance there is to JPR's concern."
Williams' fears were confirmed by former England and Lions prop Mike Burton, who said: "Drugs are a problem. It is obvious from some of the body shapes you see."
No English based players have yet tested positive for drug abuse, but Richie Griffiths, the former Wales B and South Wales Police centre, and the ex-Llanelli forward Paul Jones were both banned from playing after failing tests.Reuse content