Thanks Christine and Dr. Brown. 

BTW, the experience of being "high", "buzzed", "wasted", etc... is also called intoxication. These effects are caused by forcing nerve activity to go outside the normal physiologic range (usually intoxicants inhibit nerve activity). A buzz is the experience ofsome aspect of our brain activity going beyond the normal familiar range.

There is no sharp line between intoxication and "normal", but the intensity of a high is directly related to the dose of the drug/intoxicant used. More drug = more intoxication

Our brains have ways to "push back" against intoxication in an effort to restore the normal range in the presence of the drug. This is called "tolerance". This universal capacity shows that our brains want to be non-intoxicated. 

Unfortunately, these adaptations to the drug cause nerve activity to swing the other way when the drug is removed. This is what causes withdrawal.

But stay off the drug and the brain gradually  resets toward normal again.