Serotonin functions as a chemical messenger in the brain. It regulates mood, sleep, appetite and the emotional perception of pain. Medications that increase serotonin levels are used primarily to alleviate the symptoms associated with moderate to severe depression, including low affect and loss of pleasure in previously enjoyed activities. Newer antidepressants, known as selective serotonin reuptake inhibitors (SSRIs), elevate serotonin by blocking the chemical's recycling and inactivation. However, cells in the brain will also synthesize more serotonin under conditions where they have abundant access to the amino acid L-tryptophan and to 5-hydroxytryptophan. According to the University of Maryland Medical Center, dietary intake of these precursors might boost serotonin levels sufficiently to mitigate depression-related symptoms.
Selective Serotonin Reuptake Inhibitors
SSRIs, developed by pharmaceutical companies such as Eli Lilly (Prozac, fluoxetine), Pfizer (Zoloft, sertraline) and GlaxoSmithKline (Paxil, paroxetine), effectively manage depressive episodes in the majority of outpatients. Short-term complications of drug treatment might involve nausea or headache, whereas longer-term side effects sometimes occur with sexual health, including diminished libido and difficulty achieving orgasm. SSRI overdose can produce "serotonin syndrome," a life-threatening condition caused by excess serotonin levels. The syndrome manifests with increased body temperature, agitation and overactive reflexes that could be linked with clonic seizures. According to the Mayo Clinic, people taking SSRIs should not abruptly discontinue treatment, as they may experience serious withdrawal symptoms.
L-tryptophan, one of the least prevalent amino acids in food, converts to serotonin via a series of biochemical reactions that take place in the periphery and brain. Because oral intake can significantly boost serotonin, it is classified as a medication in Canada and Europe. Concentrated formulations go by the brand name Tryptan. L-tryptophan has to surmount various obstacles before influencing serotonin synthesis. These factors might complicate its use as an antidepressant. The amino acid must first metabolize to 5-hydroxytryptophan (5-HTP), and avoid breakdown by other metabolic pathways. Its entry into the brain is also restricted. Only small amounts can enter at any one time, and the amount that enters correlates directly with how much serotonin is produced. When employed as a supplement or medication, L-tryptophan shares some of the same liabilities as SSRIs; too much can trigger serotonin syndrome.
5-HTP, known by the brand names Cincofarm, Levothym or Oxyfan across countries in Europe, converts to serotonin in one biochemical step. This conversion can happen in the liver or brain, as 5-HTP's access to the brain is not restricted. For the purposes of supplement or drug preparation, 5-HTP is purified–exclusively–from the seeds of the African plant, Griffonia simplicifolia. Unlike L-tryptophan, it does not occur naturally in food. Side effects associated with medicinal use have not been carefully delineated.
- The University of Utah, Genetic Science Learning Center: The Serotonin Pathways
- University of Maryland Medical Center: 5-Hydroxytryptophan (5-HTP)
- Mayo Clinic: Selective Serotonin Reuptake Inhibitors (SSRIs)
- Journal of Psychiatry & Neuroscience; How to Increase Serotonin in the Human Brain without Drugs; S.N. Young; November 2007.
- Alternative Medicine Review; 5-Hydroxytryptophan: A Clinically-Effective Serotonin Precursor; T.C. Birdsall; August 1998 (Provides useful information on how serotonin is synthesized from L-tryptophan and 5-hydroxytrytophan).
- National Institute of Mental Health: Depression