Charlie Sheen Charlie Sheen

In an open letter, Charlie Sheen reveals that he embarked on a "suicide run" after learning four years ago that he was HIV-positive - news he describes as "a mule kick to my soul."

"The personal disbelief, karmic confusion, shame and anger lead to a temporary yet abysmal descent into profound substance abuse and fathomless drinking," Sheen writes. "It was a suicide run. Problem was, I'd forgotten that I'm too tough for such a cowardly departure."

Sheen published the letter on the Today show's website, hours after he sat down for a live interview with Matt Lauer on the show, during which he revealed his diagnosis.

Charlie Sheen: "I am in fact HIV-positive"

The Two and a Half Men star admits that he still hired prostitutes during this time, but insists that he "always led with condoms and honestly when it came to my condition." During his interview, Sheen told Lauer that his former wives Denise Richards and Brooke Mueller were both aware of his diagnosis. However, he claims that several other former lovers have been blackmailing him in exchange for silence about his diagnosis.

"In and around this perplexing and difficult time, I dazedly chose (or hired) the companionship of unsavory and insipid types," Sheen writes. "Sadly, my truth soon became their treason, as a deluge of blackmail and extortion took center stage in this circus of deceit."

But after his Today show appearance, Sheen says he's ready to turn over a new leaf.

"I accept this condition not as a curse or scourge, but rather as an opportunity and a challenge. An opportunity to help others. A challenge to better myself," he writes. "My partying days are behind me. My philanthropic days are ahead of me."

Read Sheen's full open letter here, and watch excerpts from his Today show interview below: