According to the Harm Reduction Coalition:
Harm reduction is a set of practical strategies that reduce negative consequences of drug use, incorporating a spectrum of strategies from safer use, to managed use to abstinence. Harm reduction strategies meet drug users "where they're at," addressing conditions of use along with the use itself.
Because harm reduction demands that interventions and policies designed to serve drug users reflect specific individual and community needs, there is no universal definition of or formula for implementing harm reduction.
That may sound largely unexceptionable, but it is radically opposed to the Bush administration's approach to illicit drug use. In the administration view, first of all, "drug abuse" is synonymous with any illegal use of drugs. Therefore, the administration concludes, the nation's most urgent "drug" problem is marijuana, because that is the substance most often used illegally. Note another implication: the dangerous entity is the drug itself, how and why it is used is irrelevant. Finally, drug abuse is a moral issue. People who use drugs illegally are criminals, and the basic response to their behavior should be punitive, i.e. they should be imprisoned. If they wish to avoid that fate, they can abstain.
This manichean world view is typical of the current administration, and we see it everywhere. A reality based view of the "drug" problem is considerably more complex. First of all, of course, the legality and illegality of drugs is in part a function of historical accident. The nation's number one drug problem, if measured by morbidity and mortality, is very obviously and indisputably tobacco. Number two is alcohol. On the other hand, there are major differences between alcohol and tobacco, perhaps the most important of which is that a moderate amount of alcohol is actually good for you. Alcohol also has positive social, cultural and aesthetic importance. Marijuana also can have important benefits for some people, and is used by millions without any evident ill effects. On the other hand, some people indeed may use both substances in ways that are harmful to themselves or others, although alcohol has far more potential for addiction and is much more dangerous.
Other illicit drugs include some that offer undeniable, major benefits to humanity, notably the opioids. These substances have a high potential for addiction, however, and can certainly cause harm. Most people are surprised to learn that most of that harm comes from the illegality of using them without a doctor's prescription. As people with chronic pain, and people on methadone maintenance prove, it is perfectly possible for humans to consume opioids for years without any major damage.
Opioid addicts suffer terrible consequences because the drugs are very expensive and somewhat difficult to obtain illegally, so satisfying addiction requires a constant search for cash, and many hours spent seeking out underworld contacts. This ruins many people financially and drives them to commit property crimes. A minority of the most desperate, who may also have pre-existing personality disorders, sometimes commit violent robberies. In order to make the most of a scarce and expensive resource, many addicts inject opioid drugs. Possession of hypodermic equipment without a prescription is also illegal in most places, which encourages people to share equipment and so transmit deadly pathogens, notably HIV and Hepatitis C. Life on the margins of society, homelessness, chronic malnutrition, and inadequate medical care, also contribute to the serious health problems suffered by many addicts.
Trafficking in illegal drugs is also a basis for violent crimes. Since illegal drug dealers cannot depend on the police and courts to enforce contracts and assure honest dealing, or to protect them from thieves, they have to be their own security guards and enforcers. The most ruthless elements of society are attracted to the trade and rise within it. Drug trafficking is associated with much of the violent crime that plagues inner cities and some rural areas. Note however that the manufacture, distribution and sale of alcohol, a powerfully addictive drug, is not associated with these problems, although it was during prohibition.
The final key point I will make here is that addiction is a remitting/relapsing condition. Most people who succeed in stopping for a time will relapse. People who are sincerely motivated to stop will typically relapse several times before they achieve long-term abstinence. As I have discussed earlier, most opioid addicts succeed only on a maintenance regimen of an opioid such as methadone, taken at a dose which does not produce euphoria but satisfies craving. People with addiction disorders must struggle with their problem for a long time. Putting them in jail as we do, in the vast majority of cases when they are not hardened criminals or significant dangers to society, is utterly counterproductive. Many people who are in jail for drug-related offenses are not even addicts, but casual marijuana users.
Needle exchange is an archetypal harm reduction policy. Through needle exchange programs, injection drug users can protect themselves, and their drug using and sexual partners, and ultimately the rest of the population, from HIV and Hepatitis C. Their used equipment is safely collected. They are brought into regular contact with outreach workers and counselors who encourage them to enter treatment and provide other counseling and assistance obtaining shelter, adequate food, and social supports essential to their prospects for recovery. It has been decisively proven that needle exchange programs do not encourage illicit drug use -- rather, they make it safer, and encourage people to get the help they need to reduce their use or stop altogether.
So why is federal policy determinedly set against needle exchange? Because drug addicts are evildoers who deserve to die. That's the only reason I can think of.