A Brief Overview of the Major Ocular Effects” discusses the wide range of ocular changes that toxic drugs can produce—ranging from mild or absent symptoms to severe vision loss resulting from endophthalmitis. This article briefly describes some of the ocular effects of commonly abused drugs. Cannabinoids Cannabis use can lead to: Conjunctival injection Mydriasis Reduced accommodation amplitude Impaired oculomotor function in chronic users Cocaine Cocaine causes pupil dilation due to inhibition of norepinephrine reuptake. At high concentrations, it may cause cycloplegia. Chronic users may also exhibit exophthalmos. Cocaine users can develop complications such as: Superficial punctate keratitis Corneal epithelial defects or erosions Corneal ulcers due to contamination from eye rubbing, retrograde passage of the substance through the nasolacrimal duct following insufflation, or direct toxic effects from the smoke Conjunctival lesions and chronic eye redness have also been reported among individuals who use crystallized heroin via the conjunctiva. Hallucinogens This group includes: LSD, psilocybin, phencyclidine (PCP), and mescaline. These drugs may cause: Hallucinations Insomnia Slurred speech CNS hyperarousal Loss of motor coordination Mydriasis Phencyclidine (PCP) does not cause changes in pupil size, but it often causes both horizontal and vertical nystagmus in intoxicated individuals. A case of oculogyric crisis induced by PCP has been reported, characterized by involuntary upward deviation of the eyes, while other ocular and systemic examinations were normal. Conclusion The use of illicit drugs is a significant public health issue. Recognizing their ocular effects is crucial for timely diagnosis and treatment. It is essential not only for general practitioners to benefit from ocular signs for early diagnosis, but also for ophthalmologists to ensure proper referral and management. Early recognition can greatly contribute to visual rehabilitation in these patients.