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Nutritional Supplement

L-Tryptophan

Also indexed as:Tryptophan

  • Pain Management

    Pain

    Double-blind research has also shown that oral L-tryptophan can increase tolerance to acute pain.
    Pain
    ×
    Other amino acids may be beneficial in reducing pain. Animal research has shown that the brain chemical serotonin is involved in pain perception,2 and some,3,4 though not all,5 preliminary human studies have reported reduced pain sensitivity when people took 2.0 to 2.75 grams per day of L-tryptophan, a precursor of serotonin. In a double-blind study, patients recovering from gallbladder surgery reported less pain when they were given L-tryptophan intravenously in the amount of 7.5 to 15 mg per 2.2 pounds body weight.6 Double-blind research has also shown that oral L-tryptophan can increase tolerance to acute pain when taken in amounts of at least 2 grams per day.7,8 Two double-blind trials found that 3 to 4 grams per day of L-tryptophan along with a low-protein, high-carbohydrate diet reduced pain in people with chronic pain.9,10 However, one controlled study did not find L-tryptophan (50 mg per 2.2 pounds of body weight per day) helpful for people with chronic pain around the temporomandibular joint.11 No research has been published investigating the pain control potential of 5-HTP (5-hydroxytryptophan), another serotonin precursor.

    Migraine Headache

    Preliminary research has found abnormally low levels of serotonin in the brains of people suffering a migraine attack, which was reversed with L-tryptophan supplements.
    Migraine Headache
    ×

    Interest in the effects of serotonin on the mechanisms of migraine has led to therapeutic trials using serotonin precursors such as L-tryptophan and 5-hydroxytryptophan (5-HTP).12 Preliminary research has found abnormally low levels of serotonin in the brains of people suffering a migraine attack, which was reversed with L-tryptophan supplements.13 A small double-blind trial found that four of eight people had fewer and less intense migraines while receiving L-tryptophan (500 mg every six hours).14 Larger double-blind trials are needed to better evaluate L-tryptophan as a migraine prevention supplement.

    In one study, 40 people with recurrent migraines received either 5-HTP (200 mg per day) or methysergide (a drug used to prevent migraines) for 40 days. Both compounds reduced the frequency of migraines by about 50%.15 Larger amounts of 5-HTP (600 mg per day) were also found to be as effective as medications for reducing migraine headache attacks in adults in two double-blind trials.16,17 Migraine attacks were reduced in frequency, severity, and duration in 90% of those taking 400 mg per day of 5-HTP in a double-blind placebo-controlled trial,18 though another trial found no benefit of 5-HTP.19 In another controlled study, 400 mg per day of DL-5-HTP (another form of 5-HTP, equivalent to 200 mg per day of 5-HTP per day led to reduced consumption of pain-killing drugs and pain scores after one to two months.20 Children who suffered from migraines and had problems sleeping had an improvement in both migraines and sleep disorders after taking 5-HTP in the amount of 20 mg for every 10 pounds of body weight in a controlled trial,21 though an earlier study showed 5-HTP had no better effect than placebo for children with migraines.22

  • Sleep Support

    Insomnia

    L-tryptophan has been used successfully for people with insomnia in many studies,including double-blind trials.
    Insomnia
    ×
    The amino acid, L-tryptophan, a serotonin precursor, taken in amounts of 1 to 4 grams at bedtime, has been used successfully for people with insomnia in many studies,23,24, including double-blind trials.25,26,27,28 Some research indicates that people with more severe forms of insomnia may need to take L-tryptophan for several nights before improvement in sleep is noticed.29,24, One controlled trial found that newborns receiving a bottle feeding in which 420 mg of L-tryptophan per 2.2 lbs of body weight had been added entered quiet sleep sooner and slept for a longer time.31 Some preliminary and controlled trials have not found L-tryptophan effective,32 or have found L-tryptophan effective only for people who awaken more frequently at night compared with those who awaken less frequently.33 Several studies combined L-tryptophan with a carbohydrate-containing meal to improve L-tryptophan uptake into the brain.26,35 A related compound that occurs naturally in the body, 5-HTP is also converted into serotonin and might, therefore, be helpful for insomnia. In a double-blind study of people without insomnia, supplementation with 5-HTP (200 mg at 9:15 p.m. and 400 mg at 11:15 p.m.) increased rapid-eye-movement (REM) sleep, presumably indicating improved sleep quality.36 In a preliminary study of people with fibromyalgia, supplementing with 100 mg of 5-HTP three times a day improved sleep quality.37 However, additional research is needed to determine whether 5-HTP is safe and effective for people with insomnia.In a preliminary study, 5-HTP was also found to be an effective treatment for "sleep terrors,"38 a common problem in children that causes sudden awakening with persistent fear or terror, screaming, sweating, confusion, and increased heart rate.

    Restless Legs Syndrome

    Preliminary research has shown some benefit reducing symptoms of restless legs syndrome and the insomnia that often accompanies it.
    Restless Legs Syndrome
    ×
    Since restless legs syndrome is often accompanied by insomnia, and L-tryptophan has been helpful for promoting sleep,37 one investigator treated two patients having both restless legs syndrome and insomnia with 1 to 2 grams of L-tryptophan at bedtime.38 In both cases restless legs symptoms improved as well as insomnia. Controlled research is needed to confirm these findings.

  • Women's Health

    Premenstrual Syndrome

    Some research suggests that L-tryptophan may help balance mood symptoms associated with PMS.
    Premenstrual Syndrome
    ×
    Preliminary research suggests that imbalances of the neurotransmitter serotonin or its precursor, L-tryptophan, may be associated with PMS.39 In a double-blind trial, women with PMS who took 6 grams per day of L-tryptophan during the second half of their menstrual cycle reported a one-third reduction in the severity of abnormal mood symptoms.40 This confirmed the results of an earlier preliminary trial in which 2 grams per day of L-tryptophan taken during the second half of the menstrual cycle reduced depression and other symptoms associated with PMS.41

    Bulimia

    L-tryptophan may be beneficial for people with bulimia, as this amino acid synthesizes serotonin, a hormone that helps regulate food intake and appetite.
    Bulimia
    ×
     

    Serotonin, a hormone that helps regulate food intake and appetite, is synthesized in the brain from the amino acid L-tryptophan. Preliminary data suggest that some people with bulimia have low serotonin levels.42 Researchers have reported that bulimic women with experimentally induced tryptophan deficiency tend to eat more and become more irritable compared to healthy women fed the same diet,43,44 though not all studies have demonstrated these effects.45

    Weight-loss diets result in lower L-tryptophan and serotonin levels in women,46 which could theoretically trigger bingeing and purging in susceptible people. However, the benefits of L-tryptophan supplementation are unclear. One small, double-blind trial reported significant improvement in eating behavior, feelings about eating, and mood among women with bulimia who were given 1 gram of L-tryptophan and 45 mg of vitamin B6 three times per day.47 Other double-blind studies using only L-tryptophan have failed to confirm these findings.48,49 L-tryptophan is available by prescription only; most drug stores do not carry it, but “compounding” pharmacies do. Most cities have at least one compounding pharmacy, which prepares customized prescription medications to meet individual patient’s needs.

    Bulimia

    Vitamin B6, when taken with L-tryptophan, has been shown to improve eating behavior, feelings about eating, and mood among women with bulimia.
    Bulimia
    ×
     

    People with eating disorders who restrict their food intake are at risk for multiple nutrient deficiencies, including protein, calcium, iron, riboflavin, niacin,50folic acid,51vitamin A, vitamin C,52 and vitamin B6,53 and essential fatty acids.54 A general multivitamin-mineral formula can reduce the detrimental health effects of these deficiencies.

    Serotonin, a hormone that helps regulate food intake and appetite, is synthesized in the brain from the amino acid L-tryptophan. Preliminary data suggest that some people with bulimia have low serotonin levels.55 Researchers have reported that bulimic women with experimentally induced tryptophan deficiency tend to eat more and become more irritable compared to healthy women fed the same diet,56,57 though not all studies have demonstrated these effects.58

    Weight-loss diets result in lower L-tryptophan and serotonin levels in women,59 which could theoretically trigger bingeing and purging in susceptible people. However, the benefits of L-tryptophan supplementation are unclear. One small, double-blind trial reported significant improvement in eating behavior, feelings about eating, and mood among women with bulimia who were given 1 gram of L-tryptophan and 45 mg of vitamin B6 three times per day.60 Other double-blind studies using only L-tryptophan have failed to confirm these findings.61,62 L-tryptophan is available by prescription only; most drug stores do not carry it, but “compounding” pharmacies do. Most cities have at least one compounding pharmacy, which prepares customized prescription medications to meet individual patient’s needs.

  • Menstrual and PMS Support

    Premenstrual Syndrome

    Some research suggests that L-tryptophan may help balance mood symptoms associated with PMS.
    Premenstrual Syndrome
    ×
    Preliminary research suggests that imbalances of the neurotransmitter serotonin or its precursor, L-tryptophan, may be associated with PMS.63 In a double-blind trial, women with PMS who took 6 grams per day of L-tryptophan during the second half of their menstrual cycle reported a one-third reduction in the severity of abnormal mood symptoms.64 This confirmed the results of an earlier preliminary trial in which 2 grams per day of L-tryptophan taken during the second half of the menstrual cycle reduced depression and other symptoms associated with PMS.65

  • Stress and Mood Management

    Depression

    Several controlled trials have found L-tryptophan as effective as antidepressant medications. Depressed people should consult a doctor before use.  
    Depression
    ×

    Disruptions in emotional well-being, including depression, have been linked to serotonin imbalances in the brain.66 L-Tryptophan is the precursor to serotonin, and low body levels of L-tryptophan are associated with depression symptoms.67 Furthermore, L-tryptophan supplements have been shown to increase serotonin levels.68  Many uncontrolled studies report that 3 to 6 grams per day of L-tryptophan helps improve mood in depressed people.69,70 Several controlled trials found that 3 to 6 grams per day of L-tryptophan were equally as effective as antidepressant medications.71,72 Some,73,74,75 though not all,76,72 double blind studies reported that similar amounts of L-tryptophan were superior to a placebo for improving depression symptoms. Trials using amounts above 6 grams per day of L-tryptophan have often found no benefit for depression, suggesting that 3 to 6 grams per day is optimum.78 5-Hydroxytryptophan (5-HTP), a breakdown product of L-tryptophan and a serotonin precursor, has also been studied as a treatment for depression. Some trials using 200 to 300 mg per day of 5-HTP with people suffering from depression have shown signs of efficacy.79,80,81,82,83,84 However, much of the research was either uncontrolled or used 5-HTP in combination with antidepressant drugs. Depressed people interested in considering 5-HTP should consult a doctor.

    Seasonal Affective Disorder

    Some research suggests that L-tryptophan alone or in combination with light therapy may improve SAD symptoms.
    Seasonal Affective Disorder
    ×
    Since disturbances of serotonin metabolism may be part of the cause of SAD,84 and creating a deficiency of L-tryptophan, a precursor of serotonin, worsens symptoms of SAD,85 L-tryptophan supplementation might be helpful. One case report describes a patient with SAD who improved after taking L-tryptophan daily, 1 gram with dinner and 1 gram at bedtime.86 In a small, preliminary study, people with SAD who responded poorly or not at all to bright light therapy were given 3 grams per day of L-tryptophan for two weeks, in addition to light therapy. Nine of 14 people responded well to this combination.87 Another small preliminary study found that one of five SAD patients that did not respond to light therapy did improve after L-tryptophan supplementation in the amount of 4 grams per day, increased to 6 grams per day if no improvement occurred at the lower dose.88 A small controlled trial found that a combination of 1.5 grams of L-tryptophan, 50 mg of vitamin B6, 300 mg vitamin C, and eight ounces of fruit juice, taken three times daily, was more effective for reducing symptoms of SAD than the same combination without L-tryptophan.895-HTP (5-hydroxytryptophan) is a substance related to L-tryptophan that also increases serotonin production and has shown antidepressant activity.90 It may also be useful in the treatment of SAD, but there is currently no research testing this possibility.

    Anxiety

    Research suggests a connection between anxiety and serotonin deficiency and that its precursur L-tryptophan may help reduce anxiety in people with social anxiety disorder and neurosis.
    Anxiety
    ×
    Animal research suggests that the brain chemical serotonin is involved in the mechanisms underlying anxiety,91 and double-blind studies have reported that creating deficiencies of L-tryptophan, a precursor of serotonin, worsens symptoms in people with anxiety disorders.92,93 A small double-blind trial tested a food bar containing 250 mg of L-tryptophan plus carbohydrate compared with a placebo bar containing only carbohydrate in a people diagnosed with social anxiety disorder.94 The bars were consumed one hour before doing a task designed to provoke anxiety, and anxiety was measured with two tests of heart rate changes and by ratings of anxiety by the participants. Only one of the two heart rate measures showed the L-tryptophan bar was more effective, and only slightly lower anxiety was reported when L-tryptophan was consumed.94 A double blind study in China reported that 3 grams per day of L-tryptophan improved symptoms, including anxiety, in a group of people diagnosed with “neurosis.”96 More research is needed to evaluate L-tryptophan as a treatment for anxiety disorders.

  • Weight Management

    Obesity

    Preliminary clinical trials suggest that serotonin precursors such as L-tryptophan might help control appetite and promote weight loss.
    Obesity
    ×
    Tryptophan is the amino acid precursor to serotonin, a neurotransmitter with a critical role in mood, appetite, and metabolic regulation.96 High serotonin levels in the brain are associated with a sense of fullness, while low levels are linked to hunger.97 Unfortunately, low-calorie diets trigger decreased serotonin signaling, deterioration of mood, increased hunger and cravings, and higher likelihood of weight regain.98 A study that included ten healthy normal-weight men found 2- and 3-gram doses of tryptophan reduced calorie intake compared to placebo when taken before a buffet-style meal,99 and in a controlled trial, increasing doses of L-tryptophan from 1 gram to 2 grams to three grams before meals resulted in progressively fewer calories and carbohydrates being consumed during the meal.100 In a crossover trial with eight participants who had chronic obesity and food cravings, taking 1 gram of L-tryptophan before each meal as part of a six-week weight loss program led to greater weight loss than placebo, but the difference was not statistically significant, partly due to the small size of the trial.101

  • Children's Health

    Attention Deficit–Hyperactivity Disorder

    Imbalances in the brain chemical serotonin, or low blood levels of its precursor, L-tryptophan, have been associated with ADHD in some (though not all) studies
    Attention Deficit–Hyperactivity Disorder
    ×
    Imbalances in the brain chemical serotonin, or low blood levels of its precursor, L-tryptophan, have been associated with ADHD in some,102 though not all,103 studies.104,105 Preliminary human studies report that creating deficiencies in L-tryptophan worsens some symptoms of ADHD. A small double blind trial found that giving children with ADHD a daily supplement of 100 mg L-tryptophan per 2.2 pounds body weight per day for one week improved behavior according to parents’ ratings, but not teachers’ ratings.106 More studies are needed to better evaluate L-tryptophan as a treatment for ADHD.

  • Heart and Circulatory Health

    Hypertension

    Supplementing with L-tryptophan can temporarily raise blood serotonin levels and lower blood pressure, but whether L-tryptophan can help prevent and manage hypertension in the long-term is still unknown.
    Hypertension
    ×
    The brain chemical serotonin may play a role in blood pressure regulation, and animal research suggests L-tryptophan, a precursor of serotonin, might be helpful in the prevention and treatment of hypertension.107 A preliminary study in 14 subjects with hypertension found 3 to 4 grams per day of L-tryptophan had an immediate blood pressure-lowering effect.108 However, because long-term use of L-tryptophan may alter serotonin metabolism, it is unclear whether it would be effective for preventing or treating high blood pressure.107 Another pilot trial reported blood pressure reductions in eight of nine volunteers with mild to moderate high blood pressure treated with 4 grams of tryptophan daily and five of eight similar subjects treated with 800 mg of 5-hydroxytryptophan (a breakdown product of tryptophan and a direct precursor of serotonin) per day.110

  • Brain Health

    Bipolar Disorder

    Supplementation with L-tryptophan has led to improvement in depression in many studies, though its effect on bipolar disorder needs more study.
    Bipolar Disorder
    ×
    L-tryptophan is the amino acid used by the body to produce serotonin, a chemical messenger important for proper brain function. Supplementation with L-tryptophan has led to improvement in depression in many studies,110,111 but information is limited about its effect on bipolar disorder. Case reports on two bipolar patients treated with lithium or an antidepressant drug described marked improvements when they were given 12 grams daily of L-tryptophan.112,113 Two trials using 6 grams of L-tryptophan daily for acute mania in patients with bipolar disorder found little or no improvement,114,115 but another double-blind, controlled study using 9.6 grams daily reported better results.116 L-tryptophan is converted to 5-HTP (5-hydroxytryptophan) before it becomes serotonin in the body. In a controlled trial, 200 mg daily of supplemental 5-HTP had antidepressant effects in bipolar patients, though it was not as effective as lithium.117 In a double-blind trial, patients with bipolar disorder had greater improvement with a combination of 5-HTP at 300 mg daily plus an antidepressant drug than with 5-HTP alone.118

    Schizophrenia

    L-tryptophan supplementation has occasionally been helpful for specific schizophrenia symptoms, such as aggression and memory function.
    Schizophrenia
    ×
    Metabolism of the amino acid L-tryptophan may be abnormal in schizophrenia,119 and initially low blood levels of L-tryptophan rise when symptoms of schizophrenia improve but remain low in cases of poor recovery.120 L-tryptophan supplementation has occasionally been helpful for specific symptoms associated with schizophrenia. A small double-blind trial found that 4 to 8 grams per day of L-tryptophan reduced aggressive symptoms.121 Another double-blind trial found 1 gram per day of L-tryptophan improved memory function in schizophrenics.122 Schizoaffective disorder has features of both schizophrenia and mood disorders. A preliminary study reported that 8 grams per day of L-tryptophan improved mood symptoms in a group of patients with schizoaffective disorder, and a small, double-blind trial found that adding 9 grams per day of L-tryptophan to drug therapy was more effective for stabilizing mood in schizoaffective disorder than drug therapy plus a placebo.123 In contrast, other symptoms of schizophrenia have not responded to L-tryptophan in amounts from 1 to 20 grams per day, according to double-blind studies.122,125 In fact, a small preliminary study reported that schizophrenic patients on a low-tryptophan diet had improved scores on certain tests of brain function and also had small improvements in psychotic symptoms.126

    Anxiety

    Research suggests a connection between anxiety and serotonin deficiency and that its precursur L-tryptophan may help reduce anxiety in people with social anxiety disorder and neurosis.
    Anxiety
    ×
    Animal research suggests that the brain chemical serotonin is involved in the mechanisms underlying anxiety,126 and double-blind studies have reported that creating deficiencies of L-tryptophan, a precursor of serotonin, worsens symptoms in people with anxiety disorders.127,128 A small double-blind trial tested a food bar containing 250 mg of L-tryptophan plus carbohydrate compared with a placebo bar containing only carbohydrate in a people diagnosed with social anxiety disorder.129 The bars were consumed one hour before doing a task designed to provoke anxiety, and anxiety was measured with two tests of heart rate changes and by ratings of anxiety by the participants. Only one of the two heart rate measures showed the L-tryptophan bar was more effective, and only slightly lower anxiety was reported when L-tryptophan was consumed.129 A double blind study in China reported that 3 grams per day of L-tryptophan improved symptoms, including anxiety, in a group of people diagnosed with “neurosis.”131 More research is needed to evaluate L-tryptophan as a treatment for anxiety disorders.
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Reliable and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.

Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.

For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.

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References

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22. Santucci M, Cortelli P, Rossi PG, et al. L-5-Hydroxytryptophan versus placebo in childhood migraine prophylaxis: a double-blind crossover study. Cephalalgia 1986;6:155-7.

23. Fitten LJ, Profita J, Bidder TG. L-tryptophan as a hypnotic in special patients. J Am Geriatr Soc 1985;33:294-7.

24. Schneider-Helmert D, Spinweber CL. Evaluation of L-tryptophan for treatment of insomnia: A review. Psychopharmacology (Berlin) 1986;89(1):1-7.

25. Demisch K, Bauer J, Georgi K, Demisch L. Treatment of severe chronic insomnia with L-tryptophan: results of a double-blind cross-over study. Pharmacopsychiatry. 1987;20:242-4.

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29. Hartmann E, Lindsley JG, Spinweber C. Chronic insomnia: effects of tryptophan, flurazepam, secobarbital, and placebo. Psychopharmacology (Berl) 1983;80:138-42.

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34. Puttini PS, Caruso I. Primary fibromyalgia syndrome and 5-hydroxy-L-tryptophan: a 90-day open study. J Int Med Res 1992;20:182-9.

35. Bruni O, Ferri R, Miano S, Verrillo E. L-5-Hydroxytryptophan treatment of sleep terrors in children. Eur J Pediatr 2004;163:402-7.

36. Kimball RW, Friedman AP, Vallejo E. Effect of serotonin in migraine patients. Neurology 1960;10:107-11.

37. Sandyk R. L-tryptophan in neuropsychiatric disorders: a review. Int J Neurosci 1992;67:127-44 [review].

38. Sandyk R. L-Tryptophan in the treatment of restless legs syndrome. Am J Psychiatry 1986;143:554-5.

39. Menkes DB, Coates DC, Fawcett JP. Acute tryptophan depletion aggravates premenstrual syndrome. J Affect Disord 1994;32:37-44.

40. Steinberg S, Annable L, Young SN, Liyanage N. A placebo-controlled clinical trial of L-tryptophan in premenstrual dysphoria. Biol Psychiatry 1999;45:313-20.

41. Steinberg S, Annable L, Young SN, Belanger MC. Tryptophan in the treatment of late luteal phase dysphoric disorder: a pilot study. J Psychiatry Neurosci 1994;19 :114-9.

42. Kaye WH, Weltzin TE. Serotonin activity in anorexia and bulimia nervosa: relationship to the modulation of feeding and mood. J Clin Psychiatry 1991;52 Suppl:41-8 [review].

43. Smith KA, Fairburn CG, Cowen PJ. Symptomatic relapse in bulimia nervosa following acute tryptophan depletion. Arch Gen Psychiatry 1999;56:171-6.

44. Weltzin TE, Fernstrom MH, Fernstrom JD, et al. Acute tryptophan depletion and increased food intake and irritability in bulimia nervosa. Am J Psychiatry 1995;152:1668-71.

45. Oldman AD, Walsh AES, Salkovskis P, et al. Biochemical and behavioural effects of acute tryptophan depletion in abstinent bulimic subjects: a pilot study. Psychol Med 1995;25:995-1001.

46. Anderson IM, Parry-Billings M, Newsholme EA, et al. Dieting reduces plasma tryptophan and alters brain 5-HT function in women. Psychol Med 1990;20:785-91.

47. Mira M, Abraham S. L-tryptophan as an adjunct to treatment of bulimia nervosa. Lancet 1989;ii:1162-3 [letter].

48. Krahn D, Mitchell J. Use of L-tryptophan in treating bulimia. Am J Psychiatry 1985;142:1130 [letter].

49. Brewerton TD, Murphy DL, Jimerson DC. Testmeal responses following m-chlorophenylpiperazine and L-tryptophan in bulimics and controls. Neuropsychopharmacology 1994;11:63-71.

50. Thibault L, Roberge AG. The nutritional status of subjects with anorexia nervosa. Int J Vitam Nutr Res 1987;57:447-52.

51. Abou-Saleh MT, Coppen A. The biology of folate in depression: implications for nutritional hypotheses of the psychoses. J Psychiatr Res 1986;20:91-101 [review].

52. Beaumont PJ, Chambers TL, Rouse L, Abraham SF. The diet composition and nutritional knowledge of patients with anorexia nervosa. J Hum Nutr 1981;35:265-73.

53. Rock CL, Vasantharajan S. Vitamin status of eating disorder patients: relationship to clinical indices and effect of treatment. Int J Eat Disord 1995;18:257-62.

54. Langan SM, Farrell PM. Vitamin E, vitamin A and essential fatty acid status of patients hospitalized for anorexia nervosa. Am J Clin Nutr 1985;41:1054-60.

55. Kaye WH, Weltzin TE. Serotonin activity in anorexia and bulimia nervosa: relationship to the modulation of feeding and mood. J Clin Psychiatry 1991;52 Suppl:41-8 [review].

56. Smith KA, Fairburn CG, Cowen PJ. Symptomatic relapse in bulimia nervosa following acute tryptophan depletion. Arch Gen Psychiatry 1999;56:171-6.

57. Weltzin TE, Fernstrom MH, Fernstrom JD, et al. Acute tryptophan depletion and increased food intake and irritability in bulimia nervosa. Am J Psychiatry 1995;152:1668-71.

58. Oldman AD, Walsh AES, Salkovskis P, et al. Biochemical and behavioural effects of acute tryptophan depletion in abstinent bulimic subjects: a pilot study. Psychol Med 1995;25:995-1001.

59. Anderson IM, Parry-Billings M, Newsholme EA, et al. Dieting reduces plasma tryptophan and alters brain 5-HT function in women. Psychol Med 1990;20:785-91.

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