The correct option is B Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Codeine is a moderately strong opiate drug that is used in pain relief and for the suppression of coughs. But strong or weak, it is still an addictive drug with many symptoms of use in common with other opiates. The road to addiction to codeine usually starts with an increasing tolerance to the drug.
Therefore, the correct answer is option B.