Yes of course, overdose of some medicince can kill you. Over dose of benzodiazepines, barbiturates, opioid, cocaine heroin are the most common cause of death due to drug overdose. Most of these medicines affect the medulla oblongata which regulates most of our vital signs.
If these medicines are taken in large quantities, it affect respiratory and cardiac centers in the medulla this can cause respiratory depression and also lead to heart failure. Coma sets in and in little or no time death comes knocking.
I advice you not to try to take overdose of these medicines because of the after effects.