Concerned — could this person be using drugs?

I am concerned for a friend. Whenever he comes around these days, he spends up to two hours in the bathroom while at the get-together and usually ends up sleeping for hours, or going home to sleep. He never stays long if he’s not sleeping or in the bathroom. He recently moved into an apartment with his girlfriend — come to find out, they broke up because according to her, she “just can’t help him anymore.” This was relayed via his brother. He and his ex are still living together even though they are not a couple. He told us he’s on medical leave from work; he’s also mentioned that he’s in a lot of debt and seeing a therapist regularly. Since he’s not working, he has been mowing lawns for money. Most recently, he came to a friend’s to mow their lawn, ended up leaving halfway through to sleep for two hours in his car, spent 45 minutes in the bathroom feeling “sick,” then up and left in the middle of a conversation(literally) to go home, leaving all his equipment strewn about the yard. He hasn’t been seeing or hearing anything as far as we now. He doesn’t have paranoid thoughts/delusions. But he’s not himself and he’s never around anymore, and we are concerned. Does this behavior sound like it involves drugs?