Not necessarily, my 14 year old is like that, and it's because they stay up all night playing video games and watching movies (it's what they do when the kids are here too, so I know that's actually what they are doing).
If you are concerned about other possible issues (like drugs/alcohol) there would likely be other signs, mood changes, behavior changes - in many cases you can tell by looking at them that something isn't quite right, or even smell it on them. There are at-home drug tests you can buy at places like CVS, and Walgreens, so if you are really worried, you can always get one of those. Though I'd try talking to your son and just asking him why he's so tired first, just to see what he has to say.
Just don't ruin yalls relationship with your kid if you find out he's smoking pot. Talk to him and show that you don't approve. Be happy he's not doing anything else if he is. Like alcohol and other heavy drugs that are addictive and dangerous. Although I have great grades and all my relationship with my mom has not been the same because she sees weed as if it's heroin and imma overdose and die or become a drug addict. If you find out he's smoking I say ground him and enforce your rules. As long as he's acting right (being polite and respectful) and not being bad or a nuisance I think he's fine. Just treat him like a son. Love him no matter what. I'm only a year older than him and see what teens are doing now a days. It's not a good world we live in. And tell him to get up and clean or somthing. Don't let him turn to a lazy a$$
My step son is 12 and he has a 10pm strict bedtime, unless it's a school night and then it's 9:30pm... I check on him on and off till about 3am when I usually go to sleep... So I know he's sleeping, but he still sleeps until 2-4pm the next day... I think it's just his age and the fact he's growing and soon entering puberty... They require a ton of sleep at this age... Don't worry unless he gives you other added reasons to worry....
He's doing the same thing with his friends that my 16 year old is doing. They stay up all night. They do it when they're here because I wake up a lot so I go to listen to them at the top of the stairs. They are laughing and oohing when one of them makes a good move on the video game.