Does L-tryptophan increase serotonin? (3+ side effects)

In this article, we will discuss whether L-tryptophan increases serotonin levels or not. Furthermore, we will explore the relationship between L-tryptophan and serotonin, what research suggests on this, the benefits of increased serotonin levels, potential side effects and precautions of using L-tryptophan and natural ways to boost serotonin. 

Does L-tryptophan increase serotonin?

Yes, L-tryptophan increases serotonin levels. L-tryptophan is considered to be the sole precursor in producing serotonin for both the central and peripheral nervous systems. (2)

L-tryptophan is an essential amino acid that your body can’t produce on its own rather you must incorporate it into your routine diet or consume supplements to meet the requirements. L-tryptophan plays a role in various physiological processes of the body including protein synthesis, which helps repair damaged body tissues. (2,4)

Serotonin is a neurotransmitter which exerts its effects by regulating a person’s overall mood, helps manage the sleep-related problem and also influence appetite to manage weight among other functions. It is known to reduce feelings of depression and anxiety. (1)

It’s important to remember that while L-tryptophan is a natural and essential component in the synthesis of serotonin, other factors including enzyme activity, co-factors and availability of nutrients also play a role in the overall regulation of serotonin levels. 

How does L-tryptophan increase serotonin levels? 

L-tryptophan being an essential amino acid is obtained through diet or supplements. It serves as a natural precursor in the synthesis of serotonin, a neurotransmitter. L-tryptophan can cross the blood-brain barrier through active transport and once after entry into the brain, it is converted into 5-hydroxytryptophan (5-HTP) with the help of an enzyme called tryptophan hydroxylase. (2)

Subsequently, this 5-HTP is ultimately broken down into serotonin. This availability of serotonin is crucial in regulating many important processes in the body. If your body does not get adequate amounts of L-tryptophan, you will most likely suffer from serotonin depletion which may disrupt and alter many physiological functions. (2,4)

If you’re considering taking supplements to boost your serotonin levels, it’s essential to consult with your healthcare provider. It’s important to keep in mind that L-tryptophan intake may not always lead to a proportional increase in serotonin levels as other factors might also be involved and individual responses can vary as everyone is unique in terms of brain chemistry. 

What does research suggest?

According to a research study, scientists carried out a clinical trial of acute tryptophan depletion (ATD) in participants to determine how reduced amounts of tryptophan affect serotonin levels and its influence on participant’s behaviour. (3)

They found out that people who were not giving tryptophan supplements and neither its dietary sources experienced more aggressive behaviour, feelings of depression and anxiety with low moods and energy as their serotonin levels were negatively influenced by unavailability of tryptophan. (3)

However, when participants started giving tryptophan supplements to boost their serotonin levels, they tended to become more friendly and less likely to get into arguments. This showed that serotonin doesn’t only affect our mood but also how we behave.

Therefore, this study concluded that increasing tryptophan levels leads to an increase in serotonin production, which in turn reduces negative feelings of a person and makes them more mentally stable. (3)

What are the benefits of increased serotonin levels?

There are several important benefits of increased serotonin levels in the brain, some of these may include the following: (4)

  • Improved mood: Sufficient levels of serotonin are effective in improving mood and boosting motivation of a person.  So the likelihood of experiencing depression is diminished in this way. 


  • Better sleep quality: Serotonin also helps in generating a hormone called melatonin, which is responsible for our sleep-wake cycle. It helps in fixing the regular sleeping schedule at appropriate times. 


  • Reduced depression and anxiety: Serotonin has a calming effect on your brain and its higher levels may help reduce feelings of anxiety, stress and depression. 


  • Appetite regulation: Serotonin also plays an important role in regulating appetite and food intake. Increased serotonin levels may help us to control cravings which contribute to weight management. 


  • Enhanced cognitive functions: Serotonin is found to be beneficial in improving focus, memory and sharp learning skills by reducing confusion and enhancing cognition. 


  • Increased social behaviour: Serotonin has shown positive influences in people dealing with social anxiety disorders by improving their self-confidence and reducing excessive fear and worry. 


  • Pain management: Higher levels of serotonin may contribute to the body’s ability to manage pain as serotonin receptors greatly influence pain perception. 


  • Improved emotional regulation: Serotonin plays a crucial role in clearing your thought patterns, making you think less negatively and improving your overall emotional well-being. Higher levels may make you more resilient and able to cope with stress. 

What are the side effects of increased serotonin from L-tryptophan?

Excessive and rapid increases in serotonin levels, be it from L-tryptophan supplements or by other means may be harmful in various ways. Here are some potential side effects and symptoms associated with increased serotonin levels:

  • Serotonin syndrome: Consuming higher doses of L-tryptophan supplements or combining them with medications that increase the levels of serotonin like certain antidepressants (Lexapro, Citalopram etc) leads to the accumulation of excessive serotonin. Its common symptoms may include fever, hallucinations, muscle rigidity, tremors, confusion, restlessness etc. (1)


  • Gastrointestinal issues: Some people may experience gastric disturbances such as nausea, vomiting or diarrhoea by overconsumption of L-tryptophan supplements. These effects are usually mild and may go away with time. 


  • Headache: Some individuals may experience mild to moderate or even severe headaches due to excessive increases in serotonin levels. 


  • Drowsiness or fatigue: Higher levels of serotonin are often associated with increased melatonin production. This hormone helps promote sleep by regulating your sleep-wake cycle. Overconsumption of L-tryptophan or taking the supplements during the daytime can make you feel more dizzy and tired. 

Natural alternatives to boost serotonin levels:

  • Include tryptophan-rich foods in your daily diet. Dietary sources are safer than supplements.
  • Exposure to sunlight can increase serotonin production. So try sunbathing for at least 15-20 minutes per day.
  • Regular exercise like running or cardio may help boost serotonin production and make you feel relaxed.
  • Practice mindfulness and other techniques to reduce or manage stress like meditation and yoga. 
  • Adequate sleep is helpful for the balanced regulation of serotonin. 
  • Incorporating certain foods in your diet which are rich in omega-3 fatty acids such as fish (salmon or trout), flaxseeds and walnuts may support serotonin function. (5)

As a pharmacist, i would suggest you to ensure regular followup appointments with your healthcare provider and proper monitoring of  serotonin levels if you’re taking L-tryptophan supplements. In case, you experience any aforementioned side effects ask your doctor to reduce the dose or stop the supplement altogether with other management strategies. 

Was this helpful?

Thanks for your feedback!