Neurological Effects of Antidepressant Overdose

Antidepressants are medications prescribed to treat depression, which the Depression and Bipolar Support Alliance says affects nearly 14.8 million Americans. There are several different types of antidepressants, but they all act by affecting the level of neurotransmitters (chemicals that send information) such as serotonin, dopamine and norepinephrine in the brain. Cyclic antidepressants are effective in treating depression because they block the binding of serotonin and norepinephrine to receptors in the brain, which increases the circulating levels of these chemicals. With too much medication, however, neurotransmitter levels can become detrimental, resulting in damage to the nerves that send signals from the brain to other parts of the body.

Extrapyramidal Symptoms

The extrapyramidal motor system is the section of the brain that contains the nerves responsible for coordinating movement. When high levels of neurotransmitters in the brain cause damage to these nerves, the result may be involuntary muscle contractions and tremors, or uncontrollable shaking that usually occurs in the hands. Other extrapyramidal symptoms include muscle rigidity, which can result in a mask-like facial expression, and drooling.

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Ophthalmoplegia

Ophthalmoplegia is weakness or paralysis of the muscles that control eye movement. In the case of an antidepressant overdose, it is caused by damage to the nerves that control the eye muscles. Because the nerves do not send correct signals to control the eye muscles, the eyes are not able to move together, causing double vision.

Seizures

A seizure is a temporary disturbance of electrical activity in the brain that results in some sort of brain dysfunction. An overdose of antidepressant medication causes a severe imbalance of chemicals in the brain that can trigger a seizure. In a study published in the American Journal of Emergency Medicine, most of the seizures experienced by overdose patients were tonic-clonic seizures (also known as grand mal seizures because they affect the entire body) that lasted less than two minutes and subsided without the aid of anti-convulsive medications.

Coma

Coma is a state of persistent unconsciousness and is often referred to as a vegetative state. Patients in a coma are alive but have lost their higher brain functions and therefore cannot interact with or respond to their surroundings. Coma induced by an overdose of cyclic antidepressant medications usually resolves within 24 hours, according to "Essentials of Emergency Medicine."