When someone has a buzz, they are mildly intoxicated, while tipsy is more being moderately intoxicated, and knowing that you are not sober anymore. Buzzed is a feeling of letting loose and losing your inhibitions just enough to have a good time, while tipsy is legally drunk. Ethanol is the component of alcohol that makes it addictive.
When you are buzzed, you still have strong physical control over yourself, and you can still make good decisions. When you are tipsy, you begin to lose physical coordination, and you also begin to have mental effects from the alcohol.
When you are buzzed, you can still legally drive your car home from the bar. However, when you are tipsy, that means legally, you shouldn’t be driving. The best way to distinguish buzzed from tipsy is by the amount of alcohol consumed.