Significant QT interval prolongation may induce severe polymorphic ventricular tachycardia called Torsade de Pointes (TdP). TdP is a type of ventricular tachycardia (VT) characterized by a twist of the QRS wave around the baseline. In some cases this leads to fatal ventricular fibrillation (VF), which is why it is of particular importance among cases of arrhythmia. QT prolongation causes TdP which may then induce fatal VF. Common causes of QT prolongation include idiosyncratic causes such as gene deficiency, drugs, and drug-drug interactions. There are many cases of QT prolongation caused by drugs used to treat noncardiac related conditions; these cases involve unintended, adverse ‘collateral’ effects. Consequently, most of the drug-related cases fall outside the scope of the doctor's area of speciality and/or expectations, which makes it difficult to take preventive and therapeutic measures. It is for this reason that it is important to identify drugs that are likely to cause QT prolongation. Here, we outline drug that may cause QT prolongation and drug-drug interaction induced QT prolongation that could cause serious arrhythmia.