Right, as the title says, I have thumb pain while playing barre chords. It makes it difficult to play them properly, considering you need to use quite a bit of pressure with your thumb to make the strings ring out clearly... Are there any ways I can stop this pain? Will it just take time to get used to? Or maybe there's something wrong with my technique?

Help. >_>
This happens to me too actually. My guitar teacher told me to make sure that I move my thumb exactly with the rest of my hand when I move the chords and also to make sure my thumb was directly behind the center of the rest of my hand. My thumb still tends to hurt, though...especially on acoustic - really only on acoustic.
Stop playing for a while. It could be tendonitis, if you keep playing you'll make it worse.
The same thing happened to me a while ago. It sucked because i couldn't play for at least 3-4weeks .If you don't want that to happen take a break and put some ice on it.
I've just started full barre chords myself I get the same thing. My tutor n friends have said it'll get less n less as your hand builds strength just dont over do it till then
Does it hurt when you do anything else or when not playing barre chords?
How do you know if it's tendonitis?
You simply MUST check out my music on
Reverbnation Downloads available here
Myspace Streaming Only

Especially for fans of Tool, APC, Avant-Garde, Ambient music, rock instrumentals, and fans of music in general. Will not disappoint.
Well, as the other guys said, it can be just a matter of taking a break, and maybe you're just not used to it. Also, maybe your acion is too high. Check the length of the gap between the fingerboard and the strings. I THINK its supposed to be approx. 2-5mm, but don't quote me on that, i'm not sure.

Also, the symptoms for Tendonitus are:

"Tendonitis symptoms can feel like a strong pulling, sharp pain when moving a joint, sharp pain when lifting or carrying anything, a deep ache, or a drawing sensation that seems to follow a straight line through the muscle into the tendon. Tendonitis can make a muscle feel as if it has lost all its strength, as if it will fail if it is called upon to lift or carry weight. These symptoms can significantly interfere with normal daily activities including those for work as well as home life."

There's a whole article at:

I had it.
Actual name is De Duervain's tendonitis. Google it.
They show a test to see if you may have it.
Hurt to do anything, even to open a soda can. Did not/barely played for about 2 months.
Don't ice, don't rest, don't play through the pain.
See a doctor.
I got a cortisone shot, played the next day, no pain since.
Don't waste your time and pain hoping it will get better. It won't.
Hope this helps.
just dont grip so hard. you dont need to use a death grip when you play the chords. also, like someone stated before, thumb positioning is a big help. try keeping your thumb behind your index finger on the back of the neck, and watch your grip. also, over gripping could de-tune your guitar.