RSI is not only painful, but can lead to loss of quality of life as ordinary tasks become painful and difficult. There are many commercial preparations out there, which will relieve the pain, however many pain killers have nasty side effects if taken long term. There are measures you can take to reduce the amount RSI you suffer, hopefully reducing the need for medicinal preparations.
Step 1) When using a keyboard and mouse, always use gel pads under your wrists. These are cheaply available in most department and computer stores, and help to prevent RSI by cushioning the vulnerable parts of your wrist instead of mashing them against a hard table.
Step 2) Consider ergonomic keyboards. They are the wacky looking ones which have been split up the middle and turned on angles, a little like butterfly wings. These keyboards place your wrists in such a manner as to give them a natural shape when typing, thus reducing the strain and likelihood of RSI.
Step 3) Take regular breaks. Although it is oft repeated, this is the best tool in your defense against RSI. It is best if you can take half hourly breaks for five minutes, although this is not always feasible in a work environment. Breaks hourly for ten minutes with stretches are fine too.
Step 4) Massage the affected joints gently at night with a soothing oil such as chamomile or lavender, it will relieve the pain as well as keeping blood flowing through the joints well.
Tips
RSI can be indicative of more serious issues such as carpal tunnel, if you find it is serious and ongoing, seek medical advice.