Anything can be a poison, it all depends on the dose. This includes the drops you use to clear your eyes.
The active, and dangerous, ingredient in many of these preparations is tetrahydrozoline hydrochloride. If ingested in sufficient amounts, it can elevate the blood pressure, drop the heart rate to dangerously low levels, reduce body temperature, and cause nausea, vomiting, shortness of breath, blurred vision, an unsteady gait, seizures, coma, and death. And you thought those little dropper bottles were harmless.
In a new case, it appears that Lana Clayton killed her husband by adding a few drops to his water over several days. He apparently fell down the stairs. Since this chemical causes walking difficulties, blurred vision, and even seizures, he could easily have staggered and fallen down the steps. Or even been pushed. Regardless, a significant amount of the chemical was found in his blood at autopsy.
I’ve blogged about this before in discussing a case of possible munch Munchausen By Proxy. Samantha Elizabeth Unger apparently poisoned her children by adding a few drops of the medication to their juice on multiple occasions. Here is the link to that post: