L-Tyrosine: Effects on Memory, Mood, ADHD, and More

Lots of people have recently become interested in whether supplementing with L-tyrosine can improve performance at work and lift mood, in part because of the opinions put forward by scientists and influencers on podcasts and social media. While tuning into commentary by these people, I’ve at times felt frustrated by their lack of depth and clarity, so in the next 2 blogs we’ll focus on what the science of L-tyrosine actually shows. The good news is that L-tyrosine can be handy in many contexts. Used intelligently, it can help you beat brain fog and more.

In this blog, we’ll focus on the effects of L-tyrosine on the brain, touching on its actions in healthy adults, mood disorders, anorexia, ADHD, and Parkinson's. Next week we’ll get into its other uses, plus some things you should consider if you want to supplement with tyrosine. Today's blog gets technical in places, so concentrate on the bullets below if you just want the highlights.

 

Key takeaways

  • L-tyrosine is an amino acid present in many foods that your body can also make from phenylalanine.
  • L-tyrosine is a precursor to the catecholamine neuromodulators, which include dopamine and noradrenaline. These are important to alertness, attention, impulse control, motivation, mood, and more.
  • When your brain is working overtime (e.g., after sleep deprivation or during very challenging tasks), it cranks through catecholamines faster than normal. Supplementing L-tyrosine can help maintain optimal catecholamine signaling at these times, supporting cognition and motivation.
  • There’s variation between people in how they respond to L-tyrosine supplementation, which might depend on individuals' traits (e.g., it seems to particularly benefit people with low motivation).
  • Supplementing L-tyrosine can lift mood in certain circumstances.
  • L-tyrosine probably doesn't meaningfully affect most cases of depression, schizophrenia, ADHD, or Parkinson's.

 

What is L-tyrosine, and what does it do?

L-tyrosine is an amino acid that is present in most foods. According to the World Health Organisation, most adults need about 1 g (14 mg per kg bodyweight) of it per day for normal bodily functions. It’s a so-called “nonessential” amino acid, for your body can make it from another amino acid named phenylalanine. However, this doesn’t mean there aren’t instances when supplementing L-tyrosine is helpful.

When you consume L-tyrosine, some of it competes with other amino acids (tryptophan, leucine, isoleucine, valine, methionine, threonine, and lysine) for transport out of the blood, into the brain. Once in the brain, L-tyrosine gets converted to L-DOPA (L-3,4-dihydroxyphenylalanine) in a reaction sped up by an enzyme named tyrosine hydroxylase. L-DOPA can then be converted into dopamine by another enzyme, and dopamine is then transformed to noradrenaline ("norepinephrine", to Americans).

I mentioned the enzyme tyrosine hydroxlase for a couple of reasons: 1) It's the rate-limiting enzyme in this pathway, meaning its activity determines the speed of the whole pathway. 2) Tyrosine hydroxlase is probably only about 75% saturated under most circumstances. This means there’s usually scope to increase dopamine and noradrenaline by providing this pathway with additional L-tyrosine, which is significant when we consider the many roles of dopamine and noradrenaline.

Dopamine, noradrenaline, and adrenaline belong to the catecholamine family of neuromodulators. Simplistically, catecholamines ready your body for activity. Widely discussed in popular culture, dopamine is involved in loads of biological processes, from control of bodily movements to resisting distractions. It’s particularly important in shaping our motivations, explaining why dysregulated dopamine signaling can drive addiction and related difficulties. Noradrenaline is the other main catecholamine neuromodulator. Like dopamine, noradrenaline has alerting and focus-enhancing effects and, relevant to this blog, noradrenaline signaling seems to help identify distractors during tasks.

Crucially, when you’re experiencing certain challenges (e.g., completing cognitively-demanding tasks in stressful conditions), neurons that release dopamine and noradrenaline become more active, firing out more of their respective neuromodulators. Since tyrosine is needed to synthesise dopamine and noradrenaline, we’d expect that supplementing with L-tyrosine can help sustain performance when your brain is working near the brink of its cognitive capacities. This is the main rationale behind using L-tyrosine as a “nootropic”.

 

L-tyrosine can help you cope with sleep loss

Some of the early research on L-tyrosine looked at its effects during sleep deprivation. The afternoon following a night without sleep, young men were given L-tyrosine, caffeine, prescription stimulant drugs (phentermine or dextroamphetamine, respectively), or a placebo. Sleep deprivation worsened performance on a range of cognitive tasks. Interestingly, L-tyrosine offset this deterioration in some tasks, perhaps because of the effects on catecholamines discussed above. Unsurprisingly, dextroamphetamine provided a greater boost than L-tyrosine, but a clear advantage of L-tyrosine is that it didn’t influence subsequent sleep, whereas the other stimulants all degraded sleep.

These results are largely in keeping with an old study that explored the effects of L-tyrosine supplementation in people with type 1 narcolepsy, a hugely disruptive sleep-wake disorder that leads to irresistible daytime sleepiness and sporadic nighttime sleep. In this experiment, 10 narcolepsy patients took L-tyrosine or placebo daily for 4 weeks. L-tyrosine didn’t affect sleep but did appear to slightly boost daytime alertness.

These positive effects on people experiencing sleep disruption underlie why military organisations are very interested in L-tyrosine. In fact, when military scientists recently completed a systematic review of supplements to maintain performance during sleep deprivation, they concluded that caffeine and L-tyrosine are the best of the bunch. (I reckon they should have included creatine for the reasons I put forward in this blog.)

 

L-tyrosine and cognitive function

L-tyrosine isn't only beneficial during sleep loss. A systematic review by Adrian Hase and his colleagues showed that L-tyrosine intake can support brain function in less extreme circumstances too. These scientists summarised the findings of studies using double-blind, placebo-controlled, crossover designs, which are relatively rigorous. They concluded that L-tyrosine supplementation prevented decrements in cognitive task performance under physically or mentally tasking conditions (5 studies). Of these experiments, 3 reported participants had better working memory when under physical stress imposed by exposure to cold temperatures. The other 2 studies found higher scores on working memory tasks that require multitasking. Regarding other cognitive faculties, there was some evidence that tyrosine improved “response inhibition”, the ability to override responses to distractions. In another study, tyrosine prevented heat stress-induced worsening of reaction times. Last, tyrosine improved the ability to find commonalities between seemingly unrelated items, which is a measure of "deep” (“convergent”) thinking. 

Studies published since Hase’s review of the research have largely supported the above findings, although they don't all point in the same direction. One study released around the time of Hase’s analysis found that tyrosine supplementation reduces “switching costs”, meaning that when people have to move from one task to another, they’re able to focus their attention on the new task faster. However, muddying the waters, more recent research suggested that during cognitively-taxing tasks, L-tyrosine supplementation worsened the ability to switch attention.

I’m not sure how we reconcile these seemingly contradictory findings, but there are nuances to the effects of L-tyrosine that influence factors such as the tasks it will be most helpful for. A study by prominent L-tyrosine researchers exemplifies this. The basis of their work is that dopamine and noradrenaline are often thought of as helping with “top-down control”, meaning they help override impulses to respond to distractions that we perceive consciously. The researchers therefore anticipated that L-tyrosine supplementation would support this ability but not affect responses to distractions perceived unconsciously. Surprisingly, they found that L-tyrosine intake doesn't always help override impulses to respond to consciously perceived distractions, instead finding that the supplement was only helpful in tasks requiring the active selection of a correct response. They also found that in specific circumstances, L-tyrosine amplified responses to distractions perceived unconsciously (the distractions were visual primes that appeared so briefly that participants didn’t consciously perceive them).  

It’s also clear that there are substantial between-person differences in their responses to tyrosine. For example, the same scientists looked at whether variation in a gene (DRD2) that encodes one of the dopamine receptor proteins associates with how people respond to tyrosine. They found that people who have a genetic variant that associates with lower dopamine activity in a part of the brain (the striatum) involved in motivation, reward, and impulse control tended to respond better to L-tyrosine supplementation than those with a variant associated with higher dopamine activity. Another study of older adults concluded that while L-tyrosine supplementation increased motivation to do a test of cognitive function in people who aren’t very impulsive by disposition, supplementation reduced motivation to do the task in people who are generally on the impulsive side. Basically, your genetics and baseline impulsivity might well determine how you respond to L-tyrosine.

Synthesising these findings, L-tyrosine can enhance several cognitive faculties related to how well you perform at work, including memory, impulsivity, task switching, reaction time, and motivation. But not all of us experience these benefits, so you'll need to do some self experimentation to figure out if L-tyrosine works for you.

 

L-tyrosine and regulation of mood and emotions

Catecholamines have many roles in mood regulation. This notion is supported by the successful development of antidepressant drugs that inhibit enzymes (monoamine oxidases) that break down catecholamines. You might therefore be wondering whether L-tyrosine intake can brighten mood. This subject hasn’t been comprehensively explored, but there is some evidence that L-tyrosine might lift mood in a few circumstances.

An unusual study had female Antarctic station researchers take L-tyrosine over the winter and the summer. In the winter, L-tyrosine intake boosted overall mood scores 47% above baseline, while the same scores fell by 136% in the placebo group. Curiously there was no effect on mood in the summer though. One possible explanation for this season-specific effect is that, at least in non-human animals, day (photoperiod) length affects brain dopamine signaling. This could explain why temporarily depleting tyrosine levels by consuming a phenylalanine- and tyrosine-deficient diet worsens mood, but this effect is greater in dim lighting than it is in bright lighting. Based on this, it’s plausible that supplementing L-tyrosine is particularly beneficial over the winter in people afflicted by seasonal affective disorder.

While some studies of L-tyrosine supplementation in healthy people have not noted obvious effects on overall mood, they have found this amino acid can affect regulation of specific emotions. One somewhat esoteric example of this might seem mega random, so understand that the researchers were trying to decipher whether catecholamines influence fear. In this experiment, healthy adults drank L-tyrosine or a placebo mixed into orange juice. After 60 mins they began a task in which a frightening stimulus was paired with a neutral stimulus. Most people learn to associate the pair of stimuli such that they soon respond fearfully when they’re only presented with the neutral stimulus. (If you’re familiar with Pavlov’s famous experiments on dogs, this Pavlovian conditioning.) While people responded as expected after placebo, drinking L-tyrosine prevented the learned expression of fear responses to the neutral stimulus. 

 

Can L-tyrosine improve mood in depression and schizophrenia?

In general, L-tyrosine supplementation does not seem to be a potent enough mood booster to meaningfully improve mood in depression. As is true of other mood disorders, there are many subtypes of depression, which can arise from different sources of dysfunction. As a result, when a group of individuals who each have unique forms of depression are given L-tyrosine and then all analysed together, any positive effects of L-tyrosine on some individuals are likely to masked by non-responders. Based on this, it's plausible that L-tyrosine supplementation could help with certain cases of depression (e.g., low mood and motivation arising from insufficient dopamine signalling) but not others, and the same might be true of schizophrenia.

 

Does L-tyrosine improve symptoms of anorexia nervosa?  

Next, there's been some work looking at L-tyrosine supplementation in anorexia nervosa. One of these studies had female patients take L-tyrosine or a placebo each day for 3 weeks, after which they crossed over into the alternative condition. L-tyrosine supplementation not only boosted mood in these patients, it also improved memory and reaction time. This is encouraging, but it's just one study.

 

Can L-tyrosine help with ADHD?

ADHD is in part be driven by dysfunction in dopamine circuits in the brain, and the most widely used medications for ADHD (e.g., Adderall, Ritalin) are highly dopaminergic. As these drugs are strong stimulants with significant side effects, there's a lot of discussion online about using dopaminergic supplements to help with ADHD.

While it seems that L-tyrosine temporarily benefits some people who have ADHD, these people are probably in the minority. Different biological processes can contribute to ADHD, and it might be that L-tyrosine best helps people with ADHD who have impaired neuromodulator metabolism. This is speculative though.

Some people have also tried combining L-tyrosine with 5-HTP (5-hydroxytryptophan) to treat ADHD. This is based in part on a study that had children with ADHD take these amino acids plus some other amino acids and vitamins. The study has since been retracted, so don’t put any stock in the results!

 

What about Parkinson's?

With respect to neurodegenerative diseases, L-tyrosine is a natural candidate to help with Parkinson's disease, which is driven by reduced dopamine signalling in several brain regions. The problem is that Parkinson's is characterised by loss of dopaminergic neurons, meaning that L-tyrosine could only influence signalling in the dwindling population of remaining neurons. What's more, Parkinson's patients appear to produce less tyrosine hydroxylase, meaning that any extra L-tyrosine consumed isn't particularly likely to be converted to L-DOPA. So it's no surprise that L-tyrosine supplementation doesn't seem to help much with Parkinson's.

 

Next time...

That’s all for now. Next time we’ll look at the effects of tyrosine on exercise performance, body temperature regulation, and thyroid health. Most important, we’ll get into how to best take L-tyrosine to reap its rewards.

Stay tuned.

Written by Greg Potter