Dilated pupils can be caused by a variety of drugs, both legal and illegal. Some of the most common drugs that cause pupil dilation include:

• Stimulants and psychotropic substances, such as cocaine, ecstasy, LSD, psilocybin, MDMA, amphetamines, cannabis, inhalants, narcotics, hallucinogens, bath salts, ketamine, and SSRI antidepressants.
• Alcohol and mescaline.
• Prescription drugs, such as prescription stimulants used in the treatment of attention-deficit/hyperactivity disorder (ADHD), selective serotonin reuptake inhibitors (SSRIs), antihistamines, anticonvulsants, anticholinergics, benzodiazepines, decongestants, dopamine precursors, and mydriatics.
• Illicit drugs, such as heroin, methamphetamine, cocaine, marijuana, ecstasy, LSD, crystal meth, ketamine, and mescaline.

It is important to note that pinpoint pupils, or pupils that get smaller and do not respond to light, are a sign of opioid use, such as heroin, oxycodone, and fentanyl. Additionally, alcohol, cocaine, and marijuana may cause bloodshot eyes since these substances cause the blood vessels around the pupils to expand. It is also worth noting that dilated pupils may occur as a result of taking prescription drugs, using Botox, experiencing emotional stress, or sustaining an injury to the eye or brain.