What is Tolerance?

Tolerance can be defined as increase in the amount of substance used in order to get the same effect, or getting a decreased effect from using the same amount of substance.  In basic terms, it means that people who use substances develop tolerance to substances as seen by increase amounts of substance use, or more frequent substance use.  Tolerance is a tell tale sign that the addiction mechanism in the body and brain has been activated.
           Why do we develop tolerance to alcohol and drugs?  Well, let's say that when you started drinking it only takes three beers to get you drunk.  After time your body (particularly your liver) releases more enzymes when you drink, so your body can become more efficient and break down the alcohol in your body quicker.  This means that you have to drink more than three beers to get drunk.  Over time, as the liver becomes more and more effecient at breaking down alcohol, you would have to drink increased amounts of alcohol to get intoxicated.
             One of the main reasons why tolerance is important to understand in early recovery is that the recovering addict, after several months of abstinence, doesn't have the same tolerance level as they did when they were using.  While they are in recovery or in a treatment center getting help, their tolerance level  drops because they are not using substances anymore, and the liver has no reason to work overtime breaking down the substances that they used before.  If an addict or alcoholic does relapse and return to the same amount of subtance use previously, and their level of tolerance has dropped, the addict could risk an overdose or alcohol poisoning.  This situation is common in early recovery.
                Another reason it is important to understand tolerance is that it is a measure of how close a person is approaching their drug "threshold".  The threshhold is the boundary that measures the amount of substance a person can take into their body before they overdose or die from the substance use.  As tolerance to a substance increases, a person gets that much closer to their threshhold.  It is very risky for a substance user or alcoholic to approach the threshold limit of substance or alcohol use.