Is repetitive drug use the cause of a bundle branch block?

Depends, of course: Most cases of bundle branch block are due to a focal injury to a key part of the heart's electrical conduction system. Coronary disease, scarring from trauma, infection, or natural processes can cause it. Some illicit drugs, especially those creating coronary spasm (e.g., cocaine, amphetamines) may create those conditions, and frequent exposure (repetitive) only exacerbates the risk.

Possible cause: Bundle branch block can be congenital or acquired. Acquired bundle branch block could be related to repetitive drug use. Whether bundle branch block is actually caused by drug use in a particular individual relates to many factors and can't be predicted for that individual without more information.