@lazyboysmum
Once his A levels are done, you need to train him up on achievable healthy eating and if he is not athletic, the need for daily exercise.
The condensed terms create a massive workload, for even the most conscientious of students. Do not underestimate the mental stress and strain. He needs to get used to preparing or choosing healthy food, or he will compromise his body's ability to deal with stress and freshers flu.
You should also consider his alcohol tolerance. My kids have been trained to drink safely from their early teens (despite having a very low household consumption).Does he know how many bottles of beer provide a pleasant effect and when he should stop? For many children, free access to alcohol for the first time occurs in freshers week. Puke in the corridors, bathrooms and missed days due to hangovers. Also regretted drunken interactions.
I honestly don't think there is a massive drugs culture (but I could be wrong). If your son has not been exposed to drug availability, he needs to think about how he will respond when these situations arise. TBH, you don;t need to get stressed about this, but if he's clear in his head beforehand, he won't make any rash decisions.