The type of drug you're looking at is a wide classification of drug called either a depressant or an "downer". Opiates, alcohol, and benbenzodiazipenall make up this drug classification.
Cocaine is a highly addictive drug which elevate levels of attention, energy and alertness, it can be seen as an stimulant because of these effects.
This drug blocks certain neurotransmitters like dopamine, serotonin and norepinephrine. What cocaine does is to bind to the transporters that remove the excess of these neurotransmitters, basically, cocaine cause an excess of these neurotransmitters, that's why people feel the effect of more energy and attention. Cocaine prevent the reabsorption of these transporters which causes the "increase". The final result is an amplification of these neurotransmitters, that's why this drug is highly addictive.
Lem's opinion is influenced by the mere exposure effect, wherein one develops a preference or liking for something on the basis that they are familiar with that something. Here, Lem is familiar with something at the start of the day (the detail), and he continues to like that detail at the end of the day because of this effect.
