Researchers believe that medications that act on the brain do so by affecting the way nerves transmit signals. However, each type of drug acts by a different mechanism. A variety of chemical substances in the brain serves as neurotransmitters. The most important of these neurotransmitters are serotonin, dopamine and norepinephrine, as well as acetylcholine and gamma-aminobutyric acid or GABA. Certain drugs block the action of these neurotransmitters while some mimic their actions, or affect the way the brain uses them.
Antipsychotic Drugs
A stimulatory neurotransmitter called dopamine partially controls brain activity. In psychotic illnesses, researchers believe that brain cells release too much dopamine, causing overstimulation. Antipsychotic drugs block the stimulatory actions of dopamine. According to the National Institute of Mental Health, not all antipsychotic drugs have the same effect on symptoms, and several can actually impair quality of life issues for the user.
Antiemetic Drugs
Stimulation of the vomiting center in the brain stem causes nausea and vomiting. According to the U.S. Department of Health and Human Services, this stimulation may be caused by signals sent from the part of the brain that reacts to harmful chemicals called the chemoreceptor trigger zone. Stimulation may also be caused by signals from the balancing mechanism in the ear, or from the lining of the digestive tract.
Antiemetic drugs act at one or more of the places in the body that are responsible for causing nausea and vomiting. For example, antihistamines reduce the sensitivity of the vomiting center in the brain stem. Phenothiazines prevent the center in the brain that reacts to harmful chemicals from stimulating the vomiting center. Metoclopramide blocks the stimulatory actions of the neurotransmitter dopamine and acts directly on the stomach to relax the muscles.
Stimulants
Stimulants increase brain activity by increasing the number of signals sent to other areas in the brain that control the body’s functions. According to the U.S. National Library of Medicine, stimulants increase the amount of norepinephrine and dopamine, but with side effects such as an increased respiratory and heart rate along with an increase in brain activity.
Depressants
Benzodiazepines depress signals in the brain by regulating the level of activity, and enhancing the action of the neurotransmitter GABA by fitting into receptors alongside GABA receptors. This decreases brain stimulation and has a calming and relaxing effect, making these drugs useful in the treatment of insomnia, anxiety, epilepsy and muscle spasms. Using benzodiazepines should be limited because of the risk of addiction.
Antidepressants
According to the U.S. National Library of Medicine, researchers believe that a drop in norepinephrine and serotonin, neurotransmitters found in the brain, causes depression by decreasing brain stimulation. These neurotransmitters are constantly released and reabsorbed by brain cells, and then broken down by the enzyme monoamine oxidase or MAO. Antidepressants either increase the levels of these neurotransmitters or prevent their inactivation in the brain.
References
- National Institutes of Mental Health: Not All Antipsychotics Created Equal: Analysis Reveals Important Differences
- U.S. Department of Health and Human Services, REMM: Guidelines for Use of Antiemetics
- Cleveland Clinic: ADHD: Stimulant Therapy
- National Institute on Drug Abuse: Stimulants
- U.S. National Library of Medicine, Medline Plus: Antidepressants
