PORTRUSH, Northern Ireland — Apparently, neither the diet nor the exotic coffee blend worked for Phil Mickelson on Thursday as he struggled to a disappointing 5-over 76 in the first round of the British Open at Royal Portrush.

Mickelson, before the tournament began, revealed that he’d lost more than 15 pounds during a six-day fast while on a retreat to Hawaii with his family last month.

He said he was “just not happy with the way I’ve been the last few months,’’ a span that included six missed cuts, including each of his last two tournaments — the Travelers Championship and the 3M Open.

Mickelson finished 18th at the Masters, 71st in the PGA Championship at Bethpage Black and 52nd at the U.S. Open. Now he’ll be in a battle to merely make the cut and play the weekend at Portrush.

Mickelson, who declined interview requests after his round, never got anything going Thursday, shooting 38 on both the front and back nine and posting only two birdies for the day.

“I just haven’t been at my best mentally, physically, so I’m trying to control the things I can control, which is get physically better, let myself heal, give myself time to reset and recharge,’’ Mickelson said Tuesday of his recent health kick. “I don’t know if it’s going to help my golf or not, but I feel better. That’s all I can really control right now.’’

He said before the tournament that he didn’t have any expectations that he would play well this week, that he planned to just try and enjoy the golf.

“When I don’t play well, I don’t feel good about myself,’’ he said, adding that his diet has helped him feel “much calmer, less agitated [and have] better self-esteem [and] less anxiety.’’

Days like Thursday surely challenge that.