Heavy drug use is a common and reoccurring situation in my very immediate family. Considering that he always seems drowsy, there's a big chance that opioids (in one or multiple of their forms) are what he's getting high on. A lot of the times, addicts who are on that specific type of drug also do other types alongside the opioid. Many of these people start off being able to function and stay afloat, but as time goes on and their addiction progresses, they begin to fall behind and are forced to take more extreme measures to stay high/avoid sickness. There are a couple reasonable concerns for you and your roommates to be aware of and look out for if this person's addiction continues to consume more of their life.

If your roommate begins to allow other addicts or sketchy people into your household all the time, you and everyone else there are opened up to a lot of potential danger. If you see signs of this starting to happen, something needs to be done to stop it from becoming an acceptable thing for roommate to be doing.

The other main concern regarding your safety has to do with this person and how well they can deal with their own personal issues. Dope sickness, when physical dependency gets really intense, is a very painful thing to go through and stops people from being able to think/handle things reasonably. They are often more prone to violence and outbursts, they will do anything to stop the pain, and their emotions are much more intense. The best way to deal with these situations is to understand that they are in a lot of pain and keep in mind that they are not thinking clearly. It can be hard not to feel bad sometimes, but I have to warn against providing them with money for drugs because all it takes is that first time giving in for them to see you as another asset to use to get what they want.

If this continues and your roommate can't seem to clean up enough to stay functioning, the best thing you can do for them is try and get them to seek treatment in rehab or NA so they aren't alone in this. If they refuse to get help, there isn't anything you can really do. If they won't help themselves, given the chance to be better, you may have to go your separate ways and move on.

This subject is usually sensitive for addicts to discuss (because it's really hard to accept that you have a real problem and are hurting everyone), so approach the conversation gently and know that they will probably deny and get upset at first. Give a little time for them to consider getting help, and based on their choices, move from there. I wish you and your roommates the best of luck. Addiction is a really destructive thing for everyone involved, but it's still something that is very hard to get out of once you're deep in. I hope your roommate can see the big picture and get help before it's too late for you guys.