People eat, drink, smoke or inject various chemicals for a variety of reasons.
Sometimes it is done under the direction of a physician for medical benefits. Others use the chemicals because they produce temporary relaxation or a feeling of happiness. In short, they use them as crutches to avoid dealing with life. The first problem is that these crutches don't solve anything, the problems remain. The best way to deal with troubles is to face them and conquer them, not avoid the issues.