Doctors typically do not recommend using muscle relaxants while pregnant, according to WebMD. Muscle relaxants such as carisoprodol, cyclobenzaprine, diazepam and methocarbamol work by suppressing the central nervous system. Possible side effects include addiction, dependence, dizziness, drowsiness and urination problems.
The U.S. Food and Drug Administration has not evaluated all of the drugs in the muscle relaxant category for safe use while pregnant, according to the Encyclopedia of Surgery. When pain in the lower back triggers significant muscle spasms, muscle relaxants can relieve the tension and ease the pain, notes WebMD. Muscle relaxants are most effective when taken before going to bed. Patients should never take muscle relaxants before driving or operating machinery.