Which Drugs Make People Aggressive?

“He must be on drugs,” we sometimes hear someone conclude upon witnessing aberrant behavior; often when upon a closer look at the circumstances, mental illness is more likely to blame. Drugs are implicated in a wide variety of adverse actions and behavior, often unspecified except to suggest their negative influence. Sometimes, there is indeed a link. This is especially true when it comes to drugs and violence.

Drugs and Aggression

Source: Image by Hamed Mehrnik from Pixabay

Many people equate aggression with the use of stimulant drugs, like cocaine or methamphetamine, and that correlation has been established. Yet research has also documented associations between aggression and other types of drugs, that most people would not ordinarily expect.

Berman, M. et al. established a link between morphine and aggression.[i] In their study, 28 male undergraduates were administered either a placebo or 45 mg of immediate-release oral morphine tablets, then given an opportunity to administer electric shocks to an increasingly aggressive (pseudo) opponent within a competitive reaction-time task. They found subjects in the morphine condition more willing to initiate such attacks than subjects who had received a placebo. They also found that subjects in the morphine condition reacted more aggressively at all levels of provocation.

Licata, A. et al. made a similar finding studying cocaine,[ii] which may not be as surprising, given the stimulant nature of cocaine (as opposed to morphine). Using 30 male undergraduates, they administered either a placebo, a low dose (1 mg/kg), or a high dose (2 mg/kg) of cocaine, and then gave subjects an opportunity to administer electric shocks to an increasingly aggressive (fictitious) opponent within the course of a competitive reaction-time task, as in the experiment by M. Berman et al. with morphine.

Licata et al. defined aggression by the intensity of shock each subject was willing to give his adversary. Their results found that subjects who had received a high dose of cocaine reacted more aggressively than subjects in the placebo condition, regardless of the level of provocation.

Regarding drugs with a traditionally depressive effect, Weisman, A.M. et al. studied the effects of three types of benzodiazepines on aggression.[iii] In their research, 44 medically healthy male subjects were administered either a placebo, 10 mg diazepam, 15 mg clorazepate, or 50 mg oxazepam. Using a stimulus similar to the preceding experiments, about 90 min after drug ingestion, participants were afforded the opportunity to administer electric shocks to what was presented as an increasingly provocative (fictitious) opponent during a competitive reaction-time task, as in the previous experiments. They also defined aggression as the level of shock a participant was willing to administer to his opponent.

Weisman et al. found that diazepam, but not all benzodiazepines, can elicit aggressive behavior “under controlled, laboratory conditions.” They then discussed implications regarding the clinical use of various types of benzodiazepines to tranquilize potentially assaultive patients.

Drugs and Violence: A Toxic Combination

These studies demonstrate links between illegal substances and aggressive behavior. Perhaps these links are not surprising when we consider the fact that drugs impair judgment, dull senses, and create other types of mental states that might dampen a sense of responsibility or concern for the well-being of others. But an appreciation of the risks of how different drugs influence the willingness to engage in violent behavior is essential to dispel the notion that illegal drug use is a victimless crime. In addition to fueling behavior designed to acquire money to buy drugs, such as theft, robbery, other crimes of dishonesty, or assaultive behavior, these studies indicate that even drugs not automatically thought of as anger-inducing substances may prompt aggression.