Hartley said Sunday he obtained the Adderall prescription pills from a former college friend and used them to stay awake while driving at night from Dallas to New Orleans for an offseason workout.
Hartley said he learned of the failed test in a recent letter from the league, and did not plan to appeal. The NFL considers players' drug tests confidential and does not comment.
"My sincere apology goes out," Hartley said. "There would never be anything that I would do that would try to hurt the team or definitely my reputation."
Hartley, in his second season with the Saints, said he was unaware Adderall was on the NFL's banned substance list. But he stressed that ignorance "was not an excuse."
"This is definitely a setback," said the 23-year-old Hartley. "I'm trying to start off my career the right way. This is a bump in the road, but we're going to overcome it."
Saints coach Sean Payton said Hartley's failed drug test and expected suspension was the primary reason the club signed 45-year-old kicker John Carney on Saturday night.
Hartley appeared to be the answer to reliability problems plaguing the Saints' kicking game since Carney's release after the 2006 season. The Saints went through four kickers in the last two seasons, including Olindo Mare, Martin Gramatica and Taylor Mehlhaff before settling on Hartley for the final eight games of 2008. Hartley made all 13 of his field goal attempts.
Carney, who kicked for New Orleans from 2001-06, became a free agent after spending last season with the New York Giants, allowing the Saints to bring him back.
Payton said Carney was signed with the expectation he'd kick for the first four regular season games and possibly stick around longer if he performs well.
"Look what happened last year," Payton said. "In New York, they had an injury. He came in and performed and they weren't going to change what was going good. ... That's the nature of our game."
Carney made 29 of 30 field goals of under 40 yards, and 6 of 8 from longer distances, during the 2008 regular season. His stint in New York came to a disappointing end, however, when he missed two of five field goal attempts in the Giants' 23-11 playoff loss to Philadelphia.
With young Giants kicker Lawrence Tynes returning from an injury, New York let Carney go.
Now Carney finds himself back in the Big Easy, where he still has a home.
"It's good to be back. It feels like I've been in a time warp, coming back after three years," Carney said after his first practice Sunday. "I feel great. I can't fool myself and think that I'm as good as I once was, but you train and you focus your goal on being at your best at least one day a week, and you plan on that being Sunday."
Carney, who made his NFL debut when Ronald Reagan was finishing out his final term in the White House, still has a chiseled physique. He said he intends to use his 21 years of NFL experience to help Hartley improve.
"The coaches have mentioned that my [mentoring] could help," Carney said. "I enjoy working with other specialists, especially the young ones, because when I was coming up I looked to a lot of veterans and stole as much as I could from them."
Hartley, who will be permitted to train and play throughout the preseason, said he would "take advantage of being able to be out here day in and day out with John and being able to learn everything he knows."
Hartley missed a 20-yard field goal in the Saints' preseason opening 17-7 victory over Cincinnati on Friday night, but he made a 54-yarder later in the game.
"It was good to see him the other night hit the second field goal," Payton said. "The first one, I think our timing was a little off ... but he's performed well and I'm happy with the player aside from the fact that all of a sudden now we're sitting here with a suspension. That's certainly disappointing and we should know better."
Hartley could be one of three Saints regulars suspended when the regular season opens.
Defensive ends Will Smith and Charles Grant also are expected to serve four-game suspensions stemming from positive tests for a banned diuretic last season. Grant and Smith did not serve their suspensions last season because they were under appeal.
The Saints placed LB Mark Simoneau (right triceps) on injured reserve, ending his season. This will be the second straight full season the 32-year-old reserve has missed. He had back surgery last year. ... Because of injuries to several reserve tight ends, Payton has moved rookie defensive end Jeremy Parnell to tight end and change his number from 79 to 89. The 6-foot-6, 278-pound Parnell was a basketball player at Ole Miss. The Saints signed him as an undrafted free agent. The Saints also signed a new tight end, Martrez Milner, a third-year pro who's regular season experience is limited to eight games with Atlanta in 2007.