less drunk alone than with friends

Why do I feel less drunk with my friends than alone? A couple of days ago I got drunk with my friend and his gf and I was very drunk after like 5 shots, and I knew it. Up until a point I remember how drunk I was, whereas when I’m by myself, I don’t feel as drunk. Is there some science to this or is it just the fact that when I’m alone, I don’t talk to anyone so I can’t exactly determine how drunk I am?