Preparing to interview Brian Wilson can make you fear what's ahead. The Beach Boy's battles with drugs and depression over the years have left a mark on the genius responsible for some of pop's most enduring classics: he has seen a darkness, and it has cast a long shadow. The evidence from the cuttings file is that interviews with him occasionally take unexpected turns or hit a wall of yes and no answers. So you start with an easy one. How does a day in the life of Brian Wilson go?

At the other end of the phone, the pleasant, polite man with a very loud voice – due to deafness in his right ear – answers with gusto, and we’re off.

"Most days when I am at home, I get up in the morning, I comb my hair, I brush my teeth and then I go to the deli down the street to have my breakfast before I go to the park to do my exercises. At the deli this morning a man was talking to me about Pet Sounds. When I come back to the house I sometimes go to the piano. When I'm inspired I go right to the piano: I don't waste any time."

In his pomp Wilson never wasted any time, either. But in his pomp Wilson worked himself to the bone. Between 1963 and 1966 he was involved in writing and producing 11 Beach Boys albums and a long run of singles. That crop included Pet Sounds, a record still capable of sending shivers up and down the spine. It's loaded with sunny-side-up endorphins to make you marvel at what pop music is capable of doing.

Self-imposed pressure

That would have done for most mere mortals, but Wilson wanted to go higher. He turned to acid and marijuana to amplify the creative process, and enlisted the lyricist Van

Dyke Parks

to help him take the following album,

Smile

, to another level, but Wilson cracked under the self-imposed pressure.

Smile

was abandoned, Wilson’s mental health was severely damaged, and the golden age appeared to be over.

These days Wilson still works at his trade as a songwriter, but the songs don’t come with the frequency of before. “It’s not the most difficult thing in the world to write a song, but I’m much slower now. But it’s good to make music, and it’s good to try to make music.”

When he reviews that rich seam of Beach Boys albums he hears nothing he’d change. “I don’t wish I did things differently or wish that I could do it again. I never think about that. I never go, I wish I had put more piano on that. Was I obsessive? I don’t know if I was, though I know a lot of people think that. Stuff just had to be right, you know. The creative process could happen every day of your life, so you have to be ready for it. You have to be right.”

In the 1960s Wilson was a whippersnapper in a hurry to make his mark. Writing, producing and recording two albums a year seemed to take nothing out of him. He was getting better with every turn of the dial, every day in the studio. Unlike most acts, his best music came in later years rather than at first. He felt no fear.

“When you’re younger you take things for granted,” he says. “You do take the creative process for granted, because you’re going too fast, doing too much, taking too much. Your head is swimming.”

When Wilson talks about Smile, the album that defines the highs and lows of his life, he emphasises the collaborators and the ambition behind the project. He'd worked with the English lyricist Tony Asher on Pet Sounds and decided he wanted to do something similar again.

"I clearly remember meeting Tony for the first time. He worked for an advertising agency, and I asked him if he was good at writing lyrics, so he said he'd give it a try – and we wrote Pet Sounds. I had instincts about him, and I was right.

“It was the same with Van Dyke Parks. He was very, very good at talking, he was interesting, and I said I’d like to write with him. And we did a good job.”

The pair wanted to get across what the US meant to them in 1966. "We wanted it to be a musical tour of the country, from Plymouth Rock across the nation to California and over to Hawaii. We wanted to capture the mood of early Americana across the nation and to show how it had changed. It was a huge effort to try to get that mood.

“It was mostly the two of us, young and creative, at work. We didn’t use many drugs when we were working, because drugs were scarce at that time. We wanted people to listen to this music and remember a time when they were young and everything was new and exciting. It was about youth, that spirit of joy and amazement.”

But Wilson was forced to abandon ship before the album was finished. The other Beach Boys were relieved – some had no idea what to make of the strange music that Wilson and Parks were making – and Wilson’s sad decline began in earnest.

Cocaine and heroin

He used cocaine and heroin to block out the depression and sadness in his head, although they didn’t help in the least. Staying in bed and overeating were two other ways Wilson tried to deal with the problems overtaking his life. They left him powerless when his band started to fall apart because of financial problems and infighting.

Wilson signed himself into a hospital, and had a series of treatments, but found little relief. It wasn't until 15 years later, when he was diagnosed with bipolar schizoaffective disorder, that he was able to understand where the voices in his head were coming from. By then he had been through the wringer several times – and that's without considering the questionable role of the therapist Eugene Landy on his life and career.

Wilson's renaissance of recent times is something to cheer. His second wife, Melinda Ledbetter, has played a big role in Wilson's rebirth as a performer. The fact that an audience was ready to see and salute him is also a significant factor.

In the past decade or so, apart from finally completing and releasing Smile, Wilson has toured and performed almost nonstop. "Everything about touring apart from the concert is one hell of a hard job to do," he says. "The performances are great, and I know people like them, because they keep telling me how wonderful they are."

They're also constant reminders of the gems he produced in the past. "When I hear something from Pet Sounds now I'm amazed at some of the vocals. I'm very proud of all that went into it and that it still works today. You never take something like that for granted. No, sir. No way. When you have Paul McCartney telling you that God Only Knows is his favourite song, that blows you away. It makes you very proud."

Back at home between shows, back at his piano, he waits for the great songs to come his way again. It’s not as if he has anything to prove, but he still waits for the magic to happen.

He doesn't believe collaborators are necessarily the answer. "I've had it with collaborators. I still work sometimes with Scott Bennett – he writes lyrics – but he's the only one I work with. I don't really know who would want to work with me at this stage. Young people? People my own age? I don't know. I'd be very interested if someone approached me. I'm open to that.

“But I think the solution is that I should really try to write lyrics myself. I wrote a lot of lyrics for The Beach Boys. The other band members wrote, but their lyrics weren’t as good as Van Dyke or Tony. They were just not as good as writers.”

For now it's the old days that dominate the discourse. That's what fans who flock to see him want, and it's what will be revisited when Love & Mercy, Bill Pohlad's film about Wilson, is released, later this year. Wilson likes what he has seen of the film, which features Paul Dano and John Cusack as young and old Wilson, respectively. "I'm very happy with it. The characters are fantastic, really good depictions of me and my wife."

It's time to let Wilson return to his piano and his exercises. He says he's looking forward to coming back to Ireland next month, then bids us farewell. A man who wasn't made for these times, perhaps, but is still waving at the gallery.

Brian Wilson plays Live at the Marquee, Cork, on July 4th