Olympic gold medalist Michael Phelps admits the three-month ban handed down to him by USA Swimming is justified.

The 23-year-old, who won eight gold medals at the Beijing Olympics last year, issued a public apology earlier this week after the News of the World published a photo of him inhaling from the type of glass pipe used to smoke cannabis.

While the world governing body FINA and the International Olympic Committee (IOC) backed the swimmer, his own national association chose to ban him for three months and withdraw financial support.

This was then compounded by the announcement that sponsor Kellogg would not renew their contract when it expires at the end of the month although fellow sponsors Omega, Speedo and Visa have all continued to back the swimmer.

Subway also confirmed they would continue their association with Phelps.

The furore has lasted all week and has seen Phelps question his participation at the London 2012 Games but the Baltimore swimmer has no objection to the ban.

He told CBS News: "You know it's fair - obviously from mistakes you should get punished.

"It is bad and stupid judgment and something I'll always live with, and a lesson I'll always learn from.

"Mom wasn't happy, obviously she has been supportive through it, but wasn't happy."

However, Phelps is doing what he knows best after a break following Beijing.

"I'm back in the water and doing the thing I love," he said.

The 14-time champion's suspension runs out in early May meaning he will be eligible for the World Championship trials in July if he decides to defend the seven titles he won in Melbourne in 2007.

The World Championships are being held in August in Rome.

It is not the first public embarrassment for the Olympic star who was sentenced to probation for drink-driving in 2004 and his actions have had a mixed reception.

Olympic and world champion Libby Trickett thinks Phelps was "extremely lucky" while fellow Australian Grant Hackett believes USA Swimming had to send out a message.

The former world and Olympic champion also told Australia's Daily Telegraph: "It certainly will (damage his reputation). It will be a period of time until he can get that back. It's such a shame."

The recently-retired distance swimmer, though, was adamant the incident will not take away from Phelps' feats in China last year.