Police officers provide crucial social services in upholding the laws and keeping people safe. Society expects them to be of good moral character. The problem is, people learn about life as they go, often making mistakes along the way. Drug use is a frequent theme, particularly in the experimental, early years. Drug use does not necessarily stop you from becoming a police officer, but you'll need to be honest about it, prove you're clean and perhaps wait a while before applying.
Police departments place a high emphasis on both personal integrity and physical fitness. They typically have you undergo background checks and physical exams for this reason. The formal background check may reveal any previous arrests or convictions related to substance abuse. As part of your background investigation, the department may have you take a polygraph examination. This can reveal drug use even if you never were arrested or convicted of substance-related activity. As part of the physical exam, you may have to submit to a drug test. Departments do not want people who are using drugs on the job because physical fitness and alertness is imperative to performing police functions, and because drugs impact your judgment. Furthermore, as drugs are illegal, departments want officers to follow the same regulations they are supposed to enforce -- that is, they don't want you to be hypocritical.
Even though departments want you to be able to abide by the laws you enforce and to be sound mentally and physically, they also recognize that some degree of "street smarts" -- that is, understanding of social circumstances and activity -- is necessary to be a good officer. Departments also understand that the majority of people make mistakes they regret and that people have the capacity to change. Therefore, they don't always eliminate you from consideration if you admit to some past substance use.
Policies on past drug use vary from department to department and drug by drug. For instance, in the city of South Lake Tahoe, California Police Department, you may be disqualified if you have used marijuana in the past two years; for harder drugs like ecstasy or heroin, the time frame is three years. In the Loveland, Colorado Police Department, the drug policy does not address specific drugs, applying a blanket three-year no-use condition to all substances. This department says you may be disqualified for use "beyond experimentation" but does not define experimentation limits. This also depends on the level at which you work. If you want to work at the federal level, guidelines are stricter, as pointed out by the Bureau of Labor Statistics. For example, your background check may be more extensive, or you may be tested for more substances more often. Therefore, the only real way to know if you can become a police officer in your jurisdiction despite your past drug use is to go to the department and ask.
The Bottom Line
Past drug use does not always automatically disqualify you from becoming a police officer, but you should expect drug use to be a topic in your interview and through the hiring process. No matter what department to which you apply, it is always best to be honest about what you have done -- lying to the department does not look good under any circumstances. If you have drug use in your history, you might have to wait to apply and get police training. Many departments are OK with past drug use if you can show that you have changed your ways -- that is, if a significant amount of time, usually two to three years, has passed since you participated in any drug-related activity.