Mysterious Pupil Dilation in Comparison Photos: Stress or Drugs?

Simply put – stress. Large pupils are often a typical stress response. When the body is put into a stress state and thus into an exceptional condition, this often results in a significant dilation of the pupils. The reason for this lies in the stimulation of the sympathetic nervous system, which is prompted to release the neurotransmitter norepinephrine. For the body, this means “danger” and signals increased attention, which in turn leads to pupil dilation. And what puts a person under more stress than an ongoing criminal investigation?

But what if the cause is not stress-related? Could large pupils also be a sign of drug use? In investigating various causes of large pupils, I discovered that besides stress, drug influence, medical conditions, and psychological factors can also play a role.

A particularly common type of drug use that can lead to dilated pupils is the consumption of stimulants like amphetamines or ecstasy. These substances increase dopamine levels in the brain and can thus enlarge the pupils. However, it’s important to note that large pupils alone are not a definitive sign of drug use, as they can also be caused by other factors.

The pupils, that central, black part of the eyes that enlarge or shrink under different lighting conditions to regulate the amount of incoming light, are sensitive to various influences. Drug use is one of the main causes of unusually dilated pupils. Certain substances affect the central nervous system and can thereby influence pupil size.

Examples of drugs that dilate pupils include stimulants like amphetamines, methamphetamine, and cocaine. These drugs increase the activity of neurotransmitters like dopamine, norepinephrine, and serotonin, leading to significant pupil dilation (Brensilver, Shoptaw & Heinzerling, 2013). Similarly, hallucinogens like LSD, psilocybin (magic mushrooms), and mescalin affect serotonin receptor activity in the brain, also causing large pupils (Halberstadt, 2015). Another example is MDMA, also known as ecstasy, a psychoactive stimulant and entactogen that can lead to dilated pupils through the release of serotonin, dopamine, and norepinephrine in the brain (Simmler, Liechti & Vollenweider, 2013).

Not only drugs but also medical conditions can affect pupil size. Aniridia, a rare genetic disorder where part or all of the iris is missing, inevitably leads to large pupils (Netland, Scott & Boyle, 2011). Similarly, Adie’s syndrome, a neurological disorder where one or both pupils are unusually large and slow to react to light, can alter pupil size (Kawasaki, 2009). Traumatic mydriasis occurs when an injury to the eye or head causes the pupils to dilate; this can be due to damage to the iris or the ciliary muscle (Yazici et al., 2015).

Psychological states and reactions also contribute to changes in pupil size. Stress is a clear trigger, activating the sympathetic nervous system to cause a “fight or flight” response, thus dilating the pupils (Bitsios, Szabadi, & Bradshaw, 2004). Shock states, whether emotional or physical, can also lead to this activation (Hammel et al., 2009). Anxiety and excitement, which stimulate the sympathetic nervous system, frequently result in large pupils as well (Steinhauer, Siegle, Condray, & Pless, 2004).

In practice, police officers use simple methods to check for drug influence. For instance, a flashlight is often shone into the eye of the suspect, as the behavior of the pupils in response to the light source quickly reveals potential drug use. Under normal circumstances, pupils constrict with strong light. In people under the influence of drugs, this reaction might be absent or significantly slower, which can be quickly determined in a brief examination. However, it’s essential to be aware that dilated pupils do not necessarily indicate drug use. Shock states, various diseases, and exceptional psychological situations can produce similar symptoms. To fully understand the phenomenon and avoid misunderstandings, a thorough investigation and, if necessary, medical clarification are indispensable. This prevents stress responses from being mistakenly interpreted as drug use, and vice versa.