He was an addict 10 years ago, got clean and to my knowledge has not done it since. But he's just gone away on holiday and for some reason unknown to me thought it would be ok to do one shot.
The effect seems to be that his body then wanted more, he recognised he made an error of judgment and is now feeling absolutely awful because he's having dreadful 'cold-turkey' response.
I know absolutely nothing about the use of drugs but am very scared about heroin as I know two people who died, very young from using it 
I am worried about him. He is staying with his parents and is so ashamed he's in bed and they think he's got flu - he doesn't want to tell them.