Concept:
Narcotic and psychotropic drugs have abuse potential and are regulated strictly.
Step 1: Need for security.
These medicines must be stored safely to prevent misuse, theft, and unauthorized access.
Step 2: Double-lock system.
A double-lock system provides extra security by requiring controlled access.
Step 3: Why other options are wrong.
Open shelves and general medicine storage are unsafe.
Refrigeration is needed only for drugs requiring low temperature, not for all narcotics.
Step 4: Final answer.
Therefore, narcotic and psychotropic drugs must be kept in a double-lock system.
\[
\boxed{\text{Kept in double-lock system}}
\]