The Someone You Loved singer didn't hold back on his opinion of other stars, saying their egos were "out of control" and that it was hard to meet genuine friends.
Capaldi, 26, told Metro: "The egos on a lot of people are f*****g out of control. What I’ve found is the people at the top are the nicest people because they’ve got nothing to prove.
"I find in this middle section there’s a lot of ego, there’s a lot of people who either want something out of a friendship as in, let’s just go to the pub and we don’t have to post about it, it’s not like an 'I want to be seen being friends with you' etc."
The star, who recently opened up on his Tourette's syndrome diagnosis, said the attitudes of other celebrities had left him feeling isolated and with a "bad taste" in his mouth.
Read more: Lady Leshurr charged with assault
He said he had met some nice people in the music industry, but that it was difficult to find musicians his age who really wanted to be friends without using other people's fame to be seen together.
Capaldi said he felt lucky to have met One Direction star Horan, 29, early on in his career and had become close friends with him.
He said: "Niall kind of ruined a lot of people for me because I was like, Niall’s great, he’s just a totally chilled guy and everyone must be like that, and then you meet a lot of other people and you’re like, no actually… there’s a lot of c***s in this game and Niall’s definitely not one of them."
Capaldi recently appeared on The Jonathan Ross Show, where he said he was relieved to be diagnosed with Tourette's as he had thought he had a degenerative disease.
He explained: "I do have Tourette's. I didn’t mean for it to be a big thing. I twitch a lot. My left shoulder goes up and I do this with my head. Now I am the poster boy for Tourette's. I’ll take it, I’ll gladly accept that.
"It was seven or eight months ago [that I was diagnosed]. I thought I had a degenerative disease. So to be told it was in fact that I have Tourette's, as you can imagine, was quite a relief. It’s fine. Everything works…"
Watch: Lewis Capaldi admits Tourette's diagnosis was 'quite a relief'