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10 Negative Effects of Tryptophan Deficiency

Written by Aleksa Ristic, MS (Pharmacy) | Last updated:
Puya Yazdi
Medically reviewed by
Puya Yazdi, MD | Written by Aleksa Ristic, MS (Pharmacy) | Last updated:

Tryptophan is an essential amino acid that controls mental health, sleep, cognition, appetite, and more. The body can’t produce it, so the lack of dietary sources may result in a range of unpleasant health effects and associated conditions. Read on to learn the potential dangers of tryptophan deficiency and how to prevent it.

Tryptophan Deficiency Symptoms & Associated Conditions

Tryptophan levels are a marker of nutritional status. Low or high levels don’t necessarily indicate a problem if there are no symptoms or if your doctor tells you not to worry about it.

Studies on the effects of tryptophan deficiency deplete this amino acid through a process called acute tryptophan depletion, where a patient is given a beverage of 15 different amino acids excluding tryptophan [1].

Drinking the beverage produces two effects:

  1. Stored tryptophan is decreased when the liver produces proteins [1].
  2. Other amino acids compete with tryptophan in crossing the blood-brain barrier thereby reducing the levels of tryptophan in the brain [1].

In a real-world setting, tryptophan deficiency is rare in developed countries and usually not severe enough to produce the effects described below [2].

1) Motion Sickness

A study of 76 people showed that tryptophan depletion intensifies dizziness, nausea, and the illusion of movement after induced motion sickness [3].

2) Mood Impairment

Depression worsened in healthy males after tryptophan depletion [4].

A study showed that patients with a family history of mental disorders were more likely to worsen their mood after tryptophan depletion [5].

Another study was able to show that women were more likely to feel the mood-worsening effect since gender affects serotonin production (males produce serotonin 52% faster than females) [6, 7].

3) Memory Decline

In a study of 30 patients, those with lowered tryptophan levels did worse in pattern recognition tests [8].

Another double-blind trial of 27 volunteers showed that tryptophan depletion impaired long-term memory in word recall and recognition tests [9].

Another study showed that women were more prone to these memory-damaging effects than men [10].

4) Depression Worsening

A study of 21 patients on antidepressants showed that lowering tryptophan levels caused the patients to return to their depressed states more often [11].

5) Seasonal Affective Disorder (SAD)

SAD is a disorder where the patient experiences depression based on seasons, mainly during the winter.

Two small studies found that tryptophan depletion contributes to SAD symptoms while supplementation may be beneficial [12, 13].

6) Manic Symptoms

A double-blind study of 7 bipolar patients on lithium treatment showed that after tryptophan depletion, manic symptoms reappeared [14].

7) Bulimia Nervosa Symptoms

Bulimia nervosa is a disorder of distorted body image with periods of excessive food intake followed by periods of self-induced vomiting, which is linked to changes in serotonin [15].

A study of 20 women showed that those with bulimia nervosa took in more calories (39% more) and showed increased agitation and mood irritability due to tryptophan depletion [15].

8) PMS

In a study done on 16 women with PMS, a depletion of tryptophan led to severe premenstrual symptoms, especially irritability [16].

9) Panic Disorder Worsening

A double-blind study on 22 patients with panic disorder showed that after tryptophan depletion, the patients had more anxiety and panic attacks. The controls, however, did not panic after tryptophan depletion [17].

10) Aggressive and Impulsive Behavior

A study of 12 patients with previous aggressive behavior and 12 without showed that after tryptophan depletion, those with aggressive tendencies became agitated and exhibited hostile behavior. Non-aggressive patients, however, decreased their aggression [18].

Tryptophan depletion increases impulsivity leading to aggression [19].

In a study of 22 highly and low impulsive patients with ADHD, the low impulsive patients became highly impulsive after tryptophan depletion [20].

Violent Behavior in Alcoholics

A study of 9 alcoholics with or without a history of violent impulsive behavior found that violent patients had lower tryptophan levels than the non-violent [21].

Another study showed that tryptophan levels decreased by 10% 30 minutes after alcohol consumption and up to 20 – 25% 1.5 to 2 hours after alcohol consumption [22].

Decreased serotonin due to tryptophan depletion triggered violent behaviors in alcoholic people [23].

Tryptophan Dietary Sources

Food Sources

Great food sources of tryptophan include [1]:

  • Oats
  • Bananas
  • Dried prunes
  • Milk and cheese
  • Tuna fish
  • Chicken and turkey
  • Peanuts
  • Chocolate


L-tryptophan is available in different oral supplement forms, alone or in combination with other ingredients. While the usual dosage of L-tryptophan is 500 mg, many people take more and the supplement’s instructions often recommend 3 pills before bedtime.

Due to potential drug interactions and other safety concerns, make sure to consult with your doctor before taking tryptophan supplements.

Read more about tryptophan supplementation benefits and side effects.

Where to buy tryptophan

About the Author

Aleksa Ristic

Aleksa Ristic

MS (Pharmacy)
Aleksa received his MS in Pharmacy from the University of Belgrade, his master thesis focusing on protein sources in plant-based diets.  
Aleksa is passionate about herbal pharmacy, nutrition, and functional medicine. He found a way to merge his two biggest passions—writing and health—and use them for noble purposes. His mission is to bridge the gap between science and everyday life, helping readers improve their health and feel better.


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