Answer:
While many people believe that chocolate can induce the effects of many medications, not just limited to narcotics, there have been limited researches done to give a exact answer.
However, chocolate is known to increase the production of Tryptophan, an amino acid responsible for making you feel sleepy. When people consume chocolate after taking a medication such as morphine (an opioid known for causing moderate to sever drowsiness) the effects of the Tryptophan combine with the effect of the opioid, morphine in your case, to cause a more potent effect. However, it is not actually making the medication more potent but in fact increasing the side effects.