Repetitive strain (or stress) injuries (RSI) is a common problem for professional musicians, not only for guitarists, but also for those who play the piano, the violin, the flute and similar instruments.
Some of the common injuries are Carpal Tunnel Syndrome (CTS) and Trigger Finger.
It is even worse if you combine playing an instrument with computer use or certain hobbies like knitting.
To reduce the risk of injuries, you should warm up before playing, take frequent breaks, and stretch after playing. It is also important to sit correctly and use a playing technique that minimizes the strain on your body.
Disclaimer: I am not a physician. Seek professional advice if you think you have symptoms of RSI.