There are two types of anesthetic drugs. One used for general and other for local. They are combination of different drugs to make the part of the body numb or knock down the entire body during the time of a procedure.
General anesthetic drugs are administered to know down the entire body of the person. These drugs are given during the major surgical procedure to make the person completely unaware of what is happening to him.
Local anesthetic drugs are administered to numb a part of the body. The drug blocks the nerve connecting the affected area with the brain. For example, the local anesthetic drug is administered during root canal procedure of a tooth. It blocks the nerve connecting brain to the affected area and affected person does not feel pain.
The anesthetic drugs are combination of different drugs that block the pain area from other parts of the body. This causes numbness of that area and doing any procedure with it gives doctor some convenience as the patient does not move.
Modern anesthetic drugs consists of gases such as nitrous oxide and derivatives of some other gases. All of them are inhalable gases. They work as effectively as previously used type of anesthetic drugs.
Now anesthetic experts recommend anesthesia administration through machines, which can measure the need for body of a patient for the drug. This prevents some unwanted incidents, which are associated to anesthetic drugs.
Interestingly, still there is a debate that how actually anesthetic drugs work. One viewpoint is that they dissolve some fat in the brain cells and that changes the cell activity, cutting the feeling of pain in the affected area.
A unanimous agreement or viewpoint is yet to be reached among scientists how anesthetic drugs work. It is an ongoing debate while effectiveness of these drugs remain proven on the other end.