Everything connected with movement in the body depends on muscles. From the heart pumping blood around to the bowels moving the spent food from the body, we would all be seriously inconvenienced if the muscles became so relaxed they stopped performing basic tasks like breathing. So never forget how much we depend on our muscles to keep on expanding and contracting when they should. If everything became too relaxed, we would be dead within a minute. For a moment, let's disappear into the deepest reaches of the Amazon where headhunters tip their arrows and darts with curare. All it takes is a scratch to allow the full-strength poison to enter the bloodstream, and it's almost instantaneous death. The advantage to the hunters is that the cooking process means the meat can be eaten safely. One wonders how they found out. No matter, this history demonstrates one of the problems in trying to use curare as a part of an anesthetic. If the dosage is even slightly off, patients never wake up. Today, independently of the need to sedate the patients, muscle relaxants are routinely used in certain types of surgery but, in most cases, curare has been abandoned - except by tribes in the Amazon who like to keep the traditional forms of hunting alive (there's a black market for heads, it seems).
So there are a range of drugs currently in use for relaxing muscles. However, we need to be clear on how this is to work. If you gave someone a sleeping pill, you would find their sleeping body almost perfectly relaxed. Similarly, pills coming from bottles with labels suggesting sedation, tranquilization, anti-anxiety and anti-depression would relax people. Even pills to relieve the symptoms caused by allergies can make people sleepy and so relaxed. The drugs actually labeled muscle relaxants aim to reduce the tension in muscles without putting you to sleep. However, you should notice many of the instructions given with these drugs suggest they should be used in combination with rest. This reflects the reality that most of the drugs can make you feel like closing your eyes and "resting". At this point, we need to distinguish between the neuromuscular blockers and the spasmolytics. The neuromuscular blockers are quite dangerous and are usually only used in hospitals and other supervised environments. The level of relaxation they induce approaches paralysis, as you might expect with anything that shuts down a part of the relevant brain activity. As you might judge from the name, spasmolytics are designed to produce a level of relaxation sufficient to prevent the sudden contractions of a muscle spasm. In general, these are less dangerous and can be used in the home environment.
Now we need to complete the circle. One of the major problems by many people who suffer from different muscular injuries and disorders is the loss of sleep. The greater the level of pain, the more difficult it is to get to sleep or stay asleep. So the power of any muscle relaxant to help people get a good night's sleep is actually highly desirable. People who feel more rested tend to have a more positive outlook. This means drugs like Carisoprodol are used in a wide range of situations. Indeed, it's not unknown for people to take Carisoprodol instead of antidepressants.