Justin Bieber says he has been fighting Lyme disease and mono

Canadian pop superstar Justin Bieber revealed on Wednesday that he had been battling Lyme disease and a serious case of mononucleosis but said he was overcoming his health issues.

On Instagram, Bieber noted that some people had recently criticised his appearance and suggested he was using drugs.

"They failed to realise I've been recently diagnosed with Lyme disease, not only that but had a serious case of chronic mono which affected my skin, brain function, energy and overall health," Bieber wrote.

"It's been a rough couple of years but getting the right treatment that will help treat this so far incurable disease," he added. "And I will be back and better than ever."

Bieber, 25, said his health challenges were among the topics to be chronicled on an upcoming 10-episode documentary series about his life that will be released on YouTube starting on Jan. 27.

In the past year, Bieber has written a series of Instagram posts to his 124 million followers talking about his struggles with depression, drug abuse and fame and crediting religion and wife Hailey Baldwin for his recovery.

This year, Bieber plans to release his first album in several years and embark on a North American tour. He released a single called "Yummy" last week.