This information is for people who have short-term back pain. It tells you about muscle relaxants, a treatment used for short-term back pain. It is based on the best and most up-to-date research.
Do they work?
Yes, but there are drawbacks. Muscle relaxants, such as diazepam, can ease muscle tension and pain within a few hours. But they also cause side effects. Most people taking muscle relaxants get dizzy or drowsy. There is also a risk you could get dependent on these drugs, even if you take them for a short time.
All muscle relaxants seem to work equally well.
What are they?
Muscle relaxants are drugs that relax your muscles. These drugs also make you calm and sleepy (they are sedatives). Muscle relaxants are used for people in severe pain, but only for a short period.
Doctors quite often prescribe them to relieve spasms in back muscles that could be causing pain. A spasm is when a muscle suddenly tightens uncontrollably. This can be very painful.
The muscle relaxant that doctors usually prescribe for bad back pain is called diazepam. Other drugs (with brand names) include:
How can they help?
If you have short-term back pain, muscle relaxants may help to:  
Reduce the tension in your back muscles
Reduce the amount of pain you are in
Allow you to move around more comfortably so you can get on with your day-to-day activities.
It probably doesn't matter which muscle relaxant you take. They all seem to work as well as each other in relieving pain.     These drugs are usually given only when your back pain is at its most severe, and you will be advised to take them for only a short time. 
If your doctor suggests that you take a muscle relaxant for your back pain, you may want to discuss alternatives. For example, non-steroidal anti-inflammatory drugs (NSAIDs) work as well as muscle relaxants, are less likely to have side effects, and their side effects are also less serious.
How do they work?
Doctors think that because these drugs relax muscles, they reduce any pain that might be caused by spasms or tension in the muscles of the back.
If your back hurts, you may try to avoid pain by being careful about how you move. This can cause extra tension in your back. Restricting your movements can make your back feel more uncomfortable, sore and stiff. Muscle relaxants should help because they generally make you feel more relaxed and less tense.
Can they be harmful?
These drugs can cause side effects. They can make you feel sick, dizzy, or drowsy.  This happened after just one week of treatment in up to 70 in 100 of the people in the studies we have looked at. You may not be able to drive if your treatment makes you drowsy.