Concept:
Schedule X drugs are controlled drugs with strict sale and record requirements.
Step 1: Need for control.
These drugs may have abuse potential or require strict monitoring.
Step 2: Prescription requirement.
Schedule X drugs are sold only on proper prescription.
Step 3: Record requirement.
The sale must be recorded in a special register, and duplicate prescription records are maintained.
Step 4: Final answer.
Therefore, Schedule X drug sale requires duplicate prescription and special register.
\[
\boxed{\text{Duplicate prescription and special register}}
\]