You can't make someone change but you can be honest. Maybe they'll listen. You might even talk them into getting help. The worst thing that can happen is a raging hangover. If you drink enough alcohol, fast enough, you can get an amount in your body that can kill you in only a few hours.
Drugs are a bigger problem than alcohol.
Alcohol and tobacco kill more than 50 times the number of people killed by cocaine, heroin, and every other illegal drug combined. Ten million Americans are addicted to alcohol. It is a drug. Alcohol makes you more sexy. The more you drink, the less you think.