The very fact he's snorting it at his Gran's suggests he's not taking it for recreation: he needs the hit.
Accordingly, he's likely to react in the same way an alcoholic does when downing the first mouthful of a much-needed drink.
It's not a strictly physical reaction as both cocaine and alcohol take time to reach the blood stream after ingestion. Nevertheless, when the hit is needed, the effects of introducing the substance into the body can be both immediate and significant.
He'll be a much happier bunny immediately after taking it and he'll get higher by degrees over the following half hour.