Empirical Evidence of the Effects of Amphetamine on Aggression


The effect of methamphetamine () on aggressive behavior has not been studied. However, anecdotal evidence provided by numerous judicial and clinical workers suggests a high correlation between aggressive acts and the use of drugs, most prominently stimulants such as methamphetamine. The effects of the d- and L-isomers of amphetamine on aggressive behavior have been studied in rats, mice, humans, and nonhuman primates. In this chapter we assume that the effects of methamphetamine on aggressive behavior are similar to the effects of amphetamine. This is most likely, but not necessarily the case. Speculation has been made that the potential combination of the induced psychoactive effects of amphetamines can lead to dangerous and aggressive behavior (). However, there is a body of research suggesting that high doses of amphetamine essentially reduce aggressive behavior (antiaggressive effects), while lower doses may potentiate aggressive responses. Rodents and primates are frequently used as analogous models for humans in experimentation because ethical considerations preclude the use of human subjects. Further, the brain structures of these animals are similar enough to those of humans to allow us to gather a great deal of insight into the human condition by understanding the effects of drugs in nonhuman animals. It has been shown that continued and consistent amphetamine use can sometimes result in paranoia and delusions, accompanied by other latent conditions such as mood swings and depression. It is the goal of this chapter, therefore, to illustrate the relationships between amphetamine use and intraspecies aggressive behavior.

Administration of Amphetamines to Rodent Subjects

Methodological Problems: Distinguishing between Aggressive and Defensive Reactions

A persistent problem in the pursuit of information regarding aggressive behavior is the ways in which the data are gathered and analyzed. As mentioned before, the typical methods of experimentation are isolation-induced and pain-induced aggression, as well as intruder-resident models. The problem is that both fear and anger can elicit attack. Pain-induced aggressive behavior is fear induced and thus neurologically very specific. Intruder-induced aggressive behavior is anger induced and thus neurologically very different from pain-induced aggressive behavior. There is no reason to predict that amphetamine would affect pain-induced aggressive behavior the same way it affects intruder-induced aggressive behavior.

Another difficulty worth mentioning is the interaction between behavioral categories and the confounding that may consequentially occur. One example is the decrease in immobility that is associated with amphetamine administration and the corresponding increase of escape/avoidance behaviors that may possibly arise from such escalation in locomotor activity. It seems reasonable that the stimulant effects of amphetamine could perhaps cause a sensation of irritability that would lead to higher rates of occurrence for defensive/offensive categories and otherwise confound the results for additional behavioral comparisons. It has been shown, however, that these amphetamine-related increases in motor activity are significant in regard to behavioral transitions such as avoidance and nonsocial exploration, but are not significant when transitions of attack are involved ().

Amphetamines and Their Effects on Dominance Hierarchy in Primates

Amphetamines and Their Effects on Human Aggressive Behavior

Concluding Remarks

Research shows that the effects of amphetamine on aggressive behavior are complex and are dependent on the types of variables involved. One such variable would be the kind of species used for experimentation. It can be difficult to make comparisons between species, as they tend to produce differing results and have unique brain structures. For example, in experiments involving rodent subjects, higher doses of amphetamine lead to a decrease in aggressive behavior, whereas higher doses in monkeys cause an escalation in aggression. In addition, the affiliative behavior of primate subjects clearly has biphasic effects, with rates of occurrence decreasing steadily as the dose increases (), whereas rodent subjects exhibit clear increases in social exploration along the same scale (). Such diversity between species often makes it difficult to generalize to the human population, and so carefully organized experimentation may be necessary to understand this variance.

Another complexity is the biphasic effects that amphetamine has on behavior. This dose-dependent condition can sometimes lead to difficulties in predictability since there is no clearly defined linear relationship. Even intraspecies effects can have large degrees of variance and so extensive sample sizes are necessary to gain a better perspective. It is interesting, however, that these biphasic results seemingly contradict the common belief that larger doses of amphetamine cause increases in aggressive behavior, when, in fact, it is smaller doses that elicit this condition.

When studying the effects of amphetamine on human behavior, several factors must be taken into consideration before any assumptions can be made. For example, the history of drug use of a patient, the patient’s lifestyle, and the patient’s social status and interactions are all possible influences on his or her drug habits and aggressive patterns of behavior. Wright and Klee (2001) report some interesting points in the area of amphetamine-related human aggressive behavior. For instance, correlations between amphetamine use and aggression are strongly associated with drug dealing rather than intoxication. Moreover, in regard to the subjects’ patterns of amphetamine use, there were no significant differences between those who reported aggression and the rest of the sample, and no straightforward relationship could be found between amphetamine use and one’s potential for aggressive behavior.

As one can see, the connection between amphetamine use and aggressive behavior is ambiguous and complex, with no easily discernible results. Since it is an illicit substance, the opportunities for human experimentation and research using this compound are extremely limited. Unfortunately, the only way we can obtain additional information regarding the subject is to increase the volume of current research and use larger sample sizes to enhance external validity and gain a broader perspective.

Selections from the book: “Methamphetamine Use Clinical and Forensic Aspects” (2003)