What is the meaning of having a "monkey on your back"?

I've been listening to a song called "Queen of Apology", by The Sounds, and it has the lyrics "Monkey on my back keeps me so desperately". I thought nothing of the term, just passed it off as a random line in a song.

Then recently I heard a song in the film 'Juno', called "Anyone Else but You", which had the lyrics "The monkey on your back is the latest trend".

I'm completely stumped as to what it means, can anyone shed some light on the matter for me?

it means to have some sort of bad addiction, like a drug addiction.

Tinatodder's on the right track - it's used to describe a problem that you have that's hard to get rid of, or not going away in a hurry. Generally used it means you have a bad secret or habit that you're not going to shake off in a hurry and its going to keep bothering you. Recently it's used in relation to drug habits, but it's an old saying, and for once it's a saying that actually make sense - the back would be the hardest place to try and remove something that's on you (because you can barely reach round there effectively) and a monkey would be very annoying, and persistent - not to mention probably try and dictate what you do.

To some extent, we probably all have monkeys on our backs.

Does that help?

Heh, I was wondering the same thing when I heard the song "Anyone But You."

So now I know :] thanks!

I have also heard the expression means "being on debt" or "owing a lot of money", is that true???

Isn't that a line in that song from Juno?
'the monkey on my back is the latest trend'

having a monkey on your back is a bad habit you just cant seem to shake. the song seems to be referring to the bad habit being popular...like so many of the young stars in hollywood having drug and alcohol addictions, and going into rehab after rehab...its almost like its popular or trendy to have some sort of addiction, cause "everybody's doing it" which of course I hope you know isnt really true!