How do you know when use of alcohol and other drugs has become a problem? Some people appear to become addicted almost immediately, while others may use for years without apparent consequences. The question is critical for individuals wondering about their own use -- and the families, friends and employers who care about them.

We know that certain clear characteristics mark the progression from first use to full-blown chemical dependency. Drug and alcohol professionals usually divide the process into four stages: experimentation, regular use, misuse and addiction/dependency.

In the experimentation phase, people limit the use of a substance to five times or less in their lifetime. This is the stage where many of us, usually in our teens or 20s, may have tried a drug out of curiosity, media or peer pressure -- or just to find out what it does to us. It's sometimes been described like a first date. Some people we like, some we're indifferent to, and some rub us the wrong way from the beginning. Experimenters either forget about the drug or move into the next stage.

In the second, or "user" stage, people are able to use their drug of choice now and then, even going long periods without it. They'll sometimes choose parties because they know drugs will be available, but they're never preoccupied with whether they'll get high. They may use alcohol or even marijuana regularly. They're in control of their consumption and experience few, if any, significant consequences with their jobs, relationships with others, or the law.

Significant controversy has developed around whether people can actually use certain drugs, especially marijuana, methamphetamine, crack or heroin, without moving into misuse or dependency. With some drugs, like alcohol, it seems that most people can stay in the "user" stage -- only about 20% appear to develop a more dependent relationship. A larger percentage of marijuana users (as many as 25%) become more dependent if they use the drug regularly over time. And a very high percentage (85% or more) of the people who use drugs like cocaine, heroin, and methamphetamine eventually enter the much more damaging stages of dependency.

People in the third stage, termed "misusers," usually develop a tolerance for their drug of choice. Because of physiological changes that come from regular use, there is a growing reliance on the drug to change the user's mood --but it takes more to produce the desired effect. Misusers become preoccupied with the drug and think frequently about when they will use again. Parties are often chosen for whether or not the drug of choice will be present. There is some level of discomfort if the drug is not available, and another drug, often alcohol, may be substituted.

Other indicators of misuse include:

• High levels of conflict with with spouse or other primary relationship
• Family concerns with use
• Patterns of isolation
• Irritability, restlessness or discontentment
• Unpredictable mood swings
• Legal problems
• Financial problems, including growing debt
• Job-related problems, including chronic absenteeism or lateness

People living a pattern of alcohol and other drug misuse can also have significant health problems. Many misused substances are highly toxic, leading to weight loss, hair and tooth loss, acne, lesions and life-threatening liver problems. General levels of stress tend to be very high, creating additional problems of their own.

In the fourth stage, the "chemically dependent" or "addicted" person continues to misuse substances despite continued consequences. Almost always preoccupied with the next drink, smoke, or fix, these people spend a significant amount of their time, money and energy avoiding the emotional and physical discomfort of not using. Addicts usually do not see that the consequences they're experiencing are a result of the misuse; rather, they feel that their life is such that they need alcohol and other drugs to cope with life's problems. ("You'd drink too, if you were married to my spouse/had my job" etc.) They have an overwhelming desire to recreate the physical sensation and emotions that the drug gives them. The combination of physiological craving and psychological need is one of the hallmarks of addiction.

Ironically, chemically dependent people commonly see themselves only as regular users. Then, when they misuse and experience some consequences, they attempt to control their intake for a time. Then they misuse again. This back and forth pattern is a common symptom of the last stage. All the while, each symptom found in misusers becomes more serious.

It is very important to note that people can't stay in addiction without significant assistance from the people around them. In case after case, chemically dependent people have relied on the financial and emotional support of family members, patience of friends or employers, even handouts on the street to continue their addictions. Ultimately, well- meaning people can actually keep the addict from the "precipitating crisis" -- threat of arrest or jail, separation or divorce, loss of child custody, loss of yet another job or other financial distress -- that makes them willing to make real changes.

It is extremely difficult, if not impossible, to arrest chemical dependency without such a crisis. But knowing the warning signs can make it possible for users and the people who care about them to take action -- before addiction destroys their lives.

The opinions expressed in this column are those of the writer