INTERNATIONAL INHALANT ABUSE WORKING GROUP
Consensus Statement on Classification of Inhalants
May 25, 2007 draft
Inhalant abuse is a worldwide drug abuse problem with devastating
consequences for many abusers and for the societies that need to address this
issue. Inhalant abuse is one of the least-understood, and poorly studied,
substance abuse problems. It is particularly difficult to obtain information on
specific national patterns of inhalant abuse and the similarities and differences
among countries in the nature of the problem. One of the contributing factors to
this has been with subclassification of inhalants. Despite the fact that there are
hundreds of products and chemicals that are subject to inhalant abuse, there has
been no agreement on whether they must be considered as a single group or
whether subgroupings exist. The purpose of this document is to discuss some of
the issues related to the classification of abuse inhalants and to propose some
steps which might be taken to address the classification issue.
Background
There has long been an international consensus on the subclassification of drugs
of abuse. For example, amphetamine-like stimulants, opiates, cannabis and
hallucinogens are categories that appear in nearly every survey of drug abuse
problems. Often, different groups of scientists are specialists in the study of one
or another of these classifications and drug abusers themselves may prefer one
class over another. There is evidence that etiologic factors differ among classes
of drugs as well. Thus, there could be important advances if there was strong
scientific support for the subclassification of inhalants.
Definition of inhalants
There is good consensus on what constitutes inhalant abuse. Typically, abused
inhalants are chemicals that can be self-administered as gases or vapors. The
products can be gases, liquids, aerosols or, in some cases, solids, but products
that begin as liquids or solids are vaporized and inhaled. There are historical
examples of liquids that are both inhaled and consumed orally (e.g. ether) and
there is a recent appearance of devices for alcohol inhalation, but the
overwhelming majority of abused inhalants, by definition, are inhaled. Drugs
such as crack cocaine, which is aerosolized, and cannabis, which is smoked, are
consumed by inhalation but are not generally, or usefully, classified as inhalants.
Nonetheless, the fact that cocaine and cannabis users may inhale their drugs
introduces the first source of misunderstanding in the classification of inhalants.
We offer the following definition of an abused inhalant:
Breathable chemical vapors or gases that users intentionally inhale because
of the chemicals' mind-altering effects. The substances inhaled are often
common household products that contain gases or volatile liquids.
Inhalant use research and policy study
Although there is general consensus on what types of products are subject to
inhalant abuse and there is a wide belief that the problem exists throughout the
world, this problem has often been ignored in drug abuse survey research and in
setting national an international drug control policy. Inhalant abuse is also
frequently ignored in drug abuse prevention efforts. We recommend that all
countries of the world and substance abuse experts in these countries include
inhalant abuse among their general work in the substance abuse field.
Specific abused inhalants
The number of different specific chemicals and products which can be subject to
inhalant abuse is very large. In the United States alone, some recent surveys
attempting to obtain information on specific types of abused inhalants have used
lists of over 60 different products or product types. If one adds all of the many
different brands of the same chemical products, the number becomes much
larger. If we add to this the even wider variety of abusable products throughout
the world, it becomes obvious that the diversity of abused inhalants is far greater
than is true for any other form of substance abuse. We believe that one of the
places where we can improve our understanding of inhalant abuse is to obtain
more detailed information on individual products, their patterns of use and the
geographical distribution of their use.
Classification systems for inhalants
There are several bases on which abused inhalants might be classified. To
simplify, these can be stated as follows:
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Chemically, based on structure
Form, such as gas, vapor or aerosol
Product type or intended use, such as fuels, anesthetics, cleaners, etc.
Epidemiological patterns of abuse
Pharmacological properties
There are strengths and weaknesses to each of these classification schemes.
Some of these will be discussed later. Ideally, several of these classifications
schemes could be merged to identify, for example, chemical groups that share
pharmacological properties and have distinctive patterns of use. We are not
there yet, as there is not a sufficient database on unique chemicals, their
pharmacological properties and their patterns of abuse to arrive at such a
scheme. With this in mind, we recommend caution in developing
subclassifications of inhalants that are not built upon strong scientific evidence.
This is particularly true for classifications that might have a tendency to create
enduring groupings that are subsequently shown to be premature or that only
may apply to one country or cultural group (e.g. a diagnostic subclassification of
inhalants).
Chemical classification. So far, there has been little evidence that, with a few
exceptions, chemical structure alone can confer differences in the abuse-related
effects of inhalants. The clear exception to this are the volatile nitrites, which
differ both chemically and pharmacologically from other inhalants. Historically,
different types of users preferred nitrites than preferred solvents and other
volatiles; however, this demographic difference may be eroding with time and
may not apply throughout the world. Nonetheless, many studies if inhalants have
considered volatile nitrites as a separate subclassification and there is
reasonable scientific support for this.
Form. A classification based on the form in which the product is obtained is
common in the inhalant abuse field. It may be most useful for inhalant abuse
prevention where parents and children are told what types of products to attend
to. On the other hand, classifications based on form would be uncommon in the
substance abuse field, and when it has been done, can often create many
problems. The best example is with cocaine, where the salt can be abused orally
or by injection and the base is usually used by inhaling the volatilized chemical.
Heroin is abused in many forms, as are many other drugs of abuse.
As with these other drugs of abuse, the same inhalant can be found in many
different products in different forms. Toluene, for example, is found in both liquid
forms and in aerosols. Indeed, aerosols are small droplets of chemicals that
typically vaporize as they pass into the air, so abusers of aerosols obtain both the
vapor and some of the small droplets. Thus, the distinction between aerosols
and vapors is artificial.
Product type. Many of the same problems with classification by form also apply
to classification by product type or intended use. The same chemical many be in
many types of products with many intended uses. Also, there many be too many
product types for useful classification. On the other hand, inhalant users and
consumers are most likely to know these products by their type and intended
use, so questionnaires attempting to obtain detailed information about individual
products will necessarily need to include lists of product types.
Epidemiological pattern of use. There has been very little research so far using
epidemiological methods to determine of classes of inhalants can be found
based on patterns or consequences of use. As mentioned above, there is some
evidence that nitrites might be preferred by special groups of users. Nitrous
oxide is also well known to be widely abused among health professionals, and
also may have a unique demography of use. We recommend that more research
be conducted on the epidemiology of specific inhalant products in a wide variety
of cultures to help inform the classification of inhalant based on demographics of
use.
Pharmacological properties. Most other classes of drugs of abuse are based on
grouping together those chemicals that share pharmacological effects that are
related to their abuse. Thus, the ability to produce a similar intoxication, to
produce cross-tolerance and cross-dependence and to produce distinctive
patters of abstinence symptoms serves as the primary basis for classification of
drugs of abuse. It is also well established that such a pharmacological
classification predicts epidemiologic patters of abuse. Unfortunately, there has
not been sufficient research to clearly identify pharmacological groupings of
inhalants, with the major exception of nitrites. Generally, many inhalants produce
pharmacological effects similar to those of alcohol and central nervous system
depressant drugs. Volatile general anesthetics also produce effects similar to
many abused inhalants and to depressant drugs, and these chemicals too have
been subject to abuse.
More research is needed in this area as well if progress is to be made on inhalant
classification based on pharmacology and shared effects.