Strychnine poisoning causes the muscles of the back to go into spasms, causing convulsions so intense that the body aches violently. This symptom called opisthotonus, can last up to two minutes, during which time the victim is conscious and in extreme pain. Sometimes the muscles of the face are down up in a horrifying smile of death referred to as the risus sardonicus in some older textbooks. Eventually these muscles tensions prevent the lungs from from working. Death, from either respiratory failure or exhaustion, usually follows within an hour.

In the past strychnine has been used as rat poison. At one time, there was also a plethora of strychnine-based 'tonics' available. These were usually prescribed to invalids and people recovering from long illnesses. Tiny amounts of the drug have the effect of raising the drug pressure slightly, which tends to create a general feeling of well being. Not surprisingly , accidental deaths and suicides from strychnine were fairly common. These would result if the bottle had not been shaken properly the patient would take a dose of the concentrated liquid which had accumulated at the bottom of the bottle.