Tizanidine is an andrenergic agonist, which means it activates the same nerve receptors as adrenaline, so yes, it can cause muscle spasm.
Most muscle relaxants are central acting, meaning they act on the central nervous system. The theory is that if the medication can interfere with the nerve signal to the muscle, then it won't contract as much.
This may work, but the side effects of most central muscle relaxants are similar to those of tranquilizers.
There's a non-central acting muscle relaxant I discovered a few years ago called dantrolene (Dantrium). This medication works directly on the skeletal muscle fibers, not the nervous system. It blocks some of the electrolytes that induce a muscle to contract, and for me at a moderate dose, is effective in treating a chronic dystonia or muscle contraction problem.
If you're using a muscle relaxant and don't like the side effects, ask your doc if dantrolene might be appropriate for your condition.
I as well as a couple others I know have actually experienced an increase in muscle pain from taking tizanidine.So you're not the only one.