In too high a dose
Benzodiazepines are vastly safer than barbiturates and barbiturate-like drugs because their activities stop at the upper part of the brain and do not, in therapeutic doses, extend to the respiratory centers in the midbrain.
Together with alcohol
, other depressant drugs, and in very high doses (or iv) they can and do cause problems, even without copd
. Normally, in usual doses, they don't.