Withdrawal symptoms are physical and mental effects that occur when a person stops using a substance, such as alcohol, nicotine, or opioids. These symptoms can vary in intensity and duration, depending on the substance and the individual's level of dependence. Common symptoms include anxiety, irritability, fatigue, and changes in appetite. The body reacts to the absence of the substance it has become accustomed to, leading to these uncomfortable sensations. In some cases, withdrawal can be severe and may require medical supervision, especially for substances like benzodiazepines or alcohol, where complications can arise.