They can be. Depressants work by slowing the brain's activity. During the first few days of taking a depressant, a person usually feels sleepy and uncoordinated. With continuing use, the body becomes used to these effects and they become less noticeable. This is known as tolerance, which means a person has to take more of the drug to get the same effects.
People can become physically dependent while taking prescription depressants, and to avoid uncomfortable symptoms of withdrawal, they can work with their doctor to stop taking the drugs on a slow timetable. If you have been using depressants regularly and try to suddenly stop, your brain activity might race out of control to the point where it causes seizures. It is important to note that misusing depressants can lead to both physical dependence and addiction, which is when a person continues to use a drug despite negative consequences.