Alcohol and drug abuse go hand in hand, because alcohol is essentially just another drug. People often separate alcohol from other drugs, but this is a mistake and can lead to errors in thinking and in judgment. Alcohol is a drug, and it can certainly be abused along with other drugs.
Most people who are abusing drugs will combine them with alcohol abuse in order to multiply the effects. Alcohol can pretty much mix with anything and give you increased effects. Of course this becomes dangerous at times, but most addicts will not mind this much, as it is a small risk to take in order to get a more pleasurable effect.
Anyone who continues to abuse drugs and alcohol will eventually run into tolerance issues. They will have to take more and more of the drugs in order to get the same level of high, and eventually they may even become addicted. Once this line is crossed, there is no going back to mere levels of abuse. The person is hooked for life and they can never again use drugs in moderation without going overboard at some point. If you continue to abuse alcohol and drugs then you will eventually reach this point of addiction.
Once you have reached the point of addiction, the only successful path at this point is one of abstinence. If drugs and alcohol gave meaning to your life, then you are going to have to replace that meaning through an act of creation. That means that once you get clean and sober and stop abusing drugs, then you have to create a new life for yourself or risk returning to drug and alcohol abuse. The key is that you cannot just stop the drugs and expect to live clean and sober forever. It takes a great deal of work and a great deal of effort in order to remain sober for long periods of time.
In early recovery you need to take a lot of action. This is necessary to get out of the habits of addiction and abuse. One method for doing so is to go to rehab or treatment. You can get clean and sober without doing so, but it is probably a lot tougher in most cases. Rehab gives you the break you need to make a fresh start. It also provides you with the support you need in order to get started in recovery.