When one is writing lectures, you find some interesting data. This graph shows the risk of using or having used alcohol, tobacco, cannabis and cocaine among those who use these substances across a number of countries.

What this shows is… and allowing for the difficulties in methodology in any survey (where you rely completely on self report)

• Most people who use alcohol, cannabis and tobacco start using these in their late teens.
• People start using cocaine a little later.
• It does not seem to matter which country you are in. The curves for each nation overlap each other.

The full paper is freely available.