Clark, a 12-year veteran, discussed the topic of marijuana use and the league's testing system Thursday morning on ESPN's "First Take."
"I know guys on my team who smoke," Clark said. "And it's not a situation where you think, 'Oh, these are guys trying to be cool.' These are guys who want to do it recreationally.
"A lot of it is stress relief. A lot of it is pain and medication. Guys feel like, 'If I can do this, it keeps me away from maybe Vicodin, it keeps me away from pain prescription drugs and things that guys get addicted to.' Guys look at this as a more natural way to heal themselves, to stress relieve and also to medicate themselves for pain. Guys are still going to do it."
Clark also expressed his views on Twitter.
I don't smoke marijuana. I won't smoke marijuana. The NFL shouldn't push marijuana but I'd be a fool to say that people don't use it.
- Ryan Clark (@Realrclark25) February 6, 2014
Clark also agreed with recent comments by New York Jets cornerback Antonio Cromartie, who suggested the league is waging a lost cause in banning the substance, while also saying the league's testing system isn't all that effective.
"It's 100 percent true. They're fighting a losing battle. The testing isn't stringent," Clark said. "There is one random test during OTAs and minicamps during the offseason, and everybody will be tested early in training camp. After that, there are no more tests. So guys understand the ways to get around failing a drug test."
ESPN NFL analyst Mark Brunell, joining "SportsCenter," offered a different opinion on the topic than Clark and Cromartie.
"There's really no place for marijuana in the NFL," Brunell said. "It is harmful. It hurts brain function. It hurts brain development. Marijuana can ruin lives. I'm very much against it."
Brunell, a former quarterback, also said marijuana testing should be random and that the league should conduct it more often.
Marijuana became a hot-button issue at the Super Bowl, as both teams -- the Seattle Seahawks and Denver Broncos -- hail from states that legalized marijuana. Seahawks coach Pete Carroll created headlines by saying he agreed with the notion the league should investigate medicinal marijuana to see if it can help players. Medicinal marijuana is legal in 20 states, plus the District of Columbia.
Commissioner Roger Goodell, addressing the issue last Friday at his annual Super Bowl news conference, downplayed the possibility of the league lifting marijuana from its list of banned substances.
"It is still an illegal substance on a national basis," Goodell said. "It's something that is part of the collective bargaining agreement with the players. It is questionable as to the positive impacts, in the face of the very strong evidence of the negative effects, including addictions and other issues.
"We'll continue to follow the medicine. Our experts right now are not indicating that we should change our policy in any way. We are not actively considering that at this point in time. But if it goes down the road sometime, that's something that we would never take off the table."
ESPN.com Jets reporter Rich Cimini contributed to this report.