Depression is a common illness that strikes about one in 15 Americans each year. It is the number one complaint heard by primary-care physicians, according to Richard Brown, M.D. author of Stop Depression Now (Penguin Putnam, 1995), and more than 50 percent of the American population suffers from moderate depression at least once in a lifetime.

Rather than just "getting over it," men and women who are depressed often require treatment of the illness. According to the National Institute of Mental Health, symptoms of depression may include a persistent sad or empty feeling; a loss of energy and appetite; and a lack of interest in socializing, work or hobbies. Depression can come in various forms ranging from mild to moderate or severe. Mild depression is characterized by difficulty in maintaining normal activities; moderate depression may involve impaired functioning at work or in social activities; and severe depression, which may involve delusions or hallucinations, markedly interferes with a person's ability to function normally and may lead to suicide. Genetic factors may put a person at greater risk for developing depression, and alcohol or drug use can make symptoms worse.

Current biochemical theories of depression suggest that biogenic amines may play a significant role in depression. This group of chemical compounds transmits nerve impulses across a synapse - a junction where nerve impulses pass to a neuron or another cell. Amines such as neropinephrine, serotonin and, to a lesser extent, dopamine, acetylcholine and epinephrine have been extensively studied for their roles in the pathophysiology of depression. Serotonin, in particular, has been the subject of intense research for the past 25 years.

Antidepressant medications affecting these amines include monoamine oxidase (MAO) inhibitors, tricyclic antidepressants and selective serotonin inhibitors (SSRI). MAO inhibitors increase norepinephrine levels, SSRIs block serotonin inactivation, and tricyclics enhance norepinephrine transmission. Psychotherapies combined with conventional antidepressant drugs such as Prozac and Paxil have become more widely used in the past several years and have been found to be effective remedies. However, patients have reported unpleasant side effects such as dry mouth, nausea, headache, or impaired sexual function or sleep. (For more information on the various side effects of the drugs commonly used to treat depression click here.) Because of these side effects, many patients have turned to natural treatments such as amino acid supplementation and herbal phytomedicines as an aid in treating mild depression. Popular choices include 5-hydroxytryptophan (5-HTP), SAM-e, St. John's Wort, Kava kava and Ginkgo Biloba. Researchers continue to study the benefits of these products and suggest that natural alternatives may provide fewer or less severe side effects than most conventional antidepressants drugs.

Amino Acids and Other Precursors

Amino Acids can act as neurotransmitters or precursors to other neurotransmitters such as serotonin. Supplementing with amino acids can ease symptoms of depression. Amino acids and related compounds used in the treatment of depression include L-tryptophan, L-tyrosine, L-phenylalanine and 5-HTP. Other players such as melatonin and SAM-e have also been suggested as effective antidepressant therapies.

• L-tyrosine: A precursor to norepinephrine; may be valuable to the people who do not respond to most antidepressant drugs except amphetamines.
  
  
• L-phenylalanine: Converted to tyrosine (a naturally occuring form of phenylalanine); D-phenylalanine (which does not normally occur in the body or in food) is metabolized to phenylethylamine (PEA), an amphetamine-like compound that occurs normally in the human brain and has been shown to have mood elevating effects. Studies have shown that depressed people commonly have low levels of phenylethylamine.
  
  
• 5-HTP: A close relative to tryptophan and a part of the metabolic pathway that leads to serotonin production. Studies from around the world have found that 5-HTP has true antidepressant properties.
  
  
• SAM-e: A chemical compound found in all living cells; SAM-e can be found in more than 40 biomedical processes in the body. Supplementing the diet with SAM-e in depressed patients can result in increased levels of serotonin, dopamine and phosphatides, improve binding of neurotransmitters to receptor sites and increase serotonin and dopamine activity. The key to SAM-e's effectiveness is its ability to make brain cells more responsive to neurotransmitters such as serotonin and dopamine.
  
  

Phytomedicines

Phytomedicines such as St. John's wort, kava kava and Ginkgo biloba may also have compounds that can aid in treating depression. Phytomedicines can not only serve as weak MAO inhibitors but can also help alleviate specific symptoms of depression. According to Harold H. Bloomfield, M.D., author of Healing Anxiety with Herbs (Harper Collins, 1998), anxiety and depression frequently occur in tandem. "Irritability, difficulty concentrating, indecision, guilt, fatigue, sleep and eating disturbances, and chronic aches and pains are symptoms common to both disorders," said Bloomfield. In addition, almost half of the people who suffer repeated panic attacks develop a major case of depression, which can be attributed to low levels of serotonin found in individuals who suffer from either anxiety disorders or depression. With this in mind, herbs such as kava and ginkgo, which have been proven to help with anxiety, may also help in treatment of depression.

• St. John's Wort: Researchers have discovered that this herb works like an SSRI (a class of antidepressant medication) and a weak MAO inhibitor. Numerous studies have confirmed that St. John's Wort does possess antidepressive effects in cases of mild to moderate depression.
  
  
• Kava kava: Has soothing and stress relieving qualities; studies have shown its effectiveness in treating anxiety and depression.
  
  
• Ginkgo biloba: Improves blood flow through the brain, accounting for its use as an aid in mental acuity. Appears to normalize neurotransmitter levels; a potent antioxidant that protects nervous system cells and regulates blood platelet stickiness. Studies have shown that ginkgo biloba may be used to improve mood and may be useful in conjunction withy standard antidepressants to enhance effectiveness in patients who are resistant to standard drug therapies. Another study showed ginkgo's effectiveness in decreasing sexual dysfunction problems caused by antidepressant drugs.