What Is L-Tryptophan and Does It Have Side Effects?

L-tryptophan is an amino acid. L-tryptophan supplements may lead to eosinophilia-myalgia and cause symptoms in your skin, blood, muscles, and organs.

L-tryptophan is an amino acid. Amino acids are the building blocks of proteins. This amino acid is used to make important molecules in your body — including serotonin, vitamin B6, or niacin. 

It’s both found in food and produced as a dietary supplement. Although it's a necessary nutrient, you should always talk to your doctor before starting a tryptophan supplement. These supplements can sometimes lead to significant health problems. Dietary tryptophan is always safe to consume. 

L-tryptophan is a specific type of nutrient called an essential amino acid. Your body can produce many of the amino acids that you need to survive. But you need to get nine of them from your diet. 

Other names for L-tryptophan include tryptophan and a-amino-b-[3-indollyl]-propionic acid.  

Although l-tryptophan is used to build proteins, it’s not found in all types of dietary protein. Some foods have a lot more tryptophan than others. If you’re curious about the exact amount of tryptophan in a food product, you can check nutrition labels or perform a search on the U.S. Department of Agriculture’s (USDA’s) central food database. 

Turkey is the most famous tryptophan-containing protein source. But it doesn’t contain as much tryptophan as people think. A similar serving size of chicken actually contains more tryptophan than turkey. 

Other foods that contain tryptophan include: 

• Fish
• Cottage cheese and other cheeses
• Bananas
• Eggs
• Nuts
• Avocados
• Milk
• Collard greens
• Seaweed 
• Beans
• Pumpkins 
• Peas
• Turnips
• Sunflower seeds
• Various flours — including corn, rice, and soybean flour

As long as you’re not vastly exceeding your daily protein requirements, you should never get an unhealthy amount of tryptophan from your diet. Daily protein recommendations depend on several factors like your: 

• Age 
• Sex
• Height
• Weight
• Amount of regular physical activity

For example, females between the ages of 31 and 59 need five to six ounces of protein daily, and males in the same age group need six to seven daily ounces. 

Your body digests tryptophan in your gut. The amino acid is then absorbed into your bloodstream. Depending on the state of the rest of your body, a certain amount will pass through your blood-brain barrier and enter your brain. 

Two of the most important compounds your body makes with tryptophan are the neurotransmitter serotonin and the B vitamin known as niacin or vitamin B6. 

Serotonin transmits chemical signals throughout your nervous system. It plays a large number of roles in your body. For example, it promotes feelings of happiness, calmness, and relaxation. It can modify your appetite and relieve pain. It’s also used to make melatonin which helps regulate your sleeping patterns. 

Niacin also has many uses throughout your body. It helps your digestion and is used to maintain healthy skin and nerves. 

L-tryptophan supplements were first produced in the 1980s because they supposedly help people fall asleep. To this day, this specific use hasn’t been proven. But preliminary data is encouraging. 

Then the USDA banned the supplements in 1990. Approximately 5,000 people taking the supplements had come down with a serious condition called eosinophilia-myalgia (ESM). This condition leads to a wide range of symptoms in your: 

• Skin
• Blood
• Muscles
• Organs 

It can even lead to death. Specifically, 37 people died before the USDA banned the products. But this complication was likely not a direct result of the tryptophan. 

Instead, it was probably caused by some contaminant — like 4,5-tryptophan-dione. This contaminant is found in small amounts in a variety of tryptophan supplement samples. However, no scientific data has confirmed whether or not it can cause ESM.  

Then — in 2005 — the FDA again allowed for the sale of L-tryptophan supplements. But they are not safe to take unless you’re under your doctor’s supervision. High levels may cause liver and brain toxicity. 

L-tryptophan supplements can also negatively interfere with several prescription medications, including: 

• Antidepressants
• Monoamine oxidase inhibitors
• Linezolid
• Carbidopa

Make sure to talk to your doctor if you’re not sure whether or not your prescription falls into one of these categories.   

You may encounter a lot of fantastic-sounding health claims about the powers of tryptophan supplements. Most of these have not been definitively proven through rigorous scientific studies. But research is ongoing, and new data is available regularly. 

Over time many of these claims could become verified scientific facts. 

Some initial claims that you may see about tryptophan supplements include its ability: 

• As a natural antidepressant
• To treat hyperactive children
• To calm manic episodes in people with bipolar disorder
• To relieve severe PMS symptoms

Several studies have attempted to figure out whether or not tryptophan can help you fall asleep and induce a more relaxed mood. Research indicates that large amounts taken at the right time can have these positive effects. 

But it’s likely not the turkey at your thanksgiving meal that’s making you so sleepy. During that meal, you’re eating so many different nutrients that tryptophan doesn’t significantly impact your body. Eating potent sources of tryptophan on an empty stomach an hour before bed will likely help make you sleepy. 

Small studies conducted with tryptophan-rich extracts also indicate a positive effect on people’s moods. 

Additionally, ongoing human trials show that it may slow the progression of chronic kidney disease.    

One of the more interesting uses for tryptophan is as a biomarker for the presence of specific health problems. This means that by looking at tryptophan levels in certain body parts, researchers can get a clue as to what your underlying health complications may be. 

For example: 

• Imaging the tryptophan in your eyes may be able to help your doctor diagnose the presence and stage of cataracts
• People with high levels of tryptophan in their blood also had higher blood pressure and insulin resistance — this could be a sign that you’re close to developing type II diabetes or a heart problem
• People with Crohn’s disease have consistently low levels of tryptophan in their blood — this could help researchers both better diagnose and understand this condition

Overall, there’s no denying that l-tryptophan plays a crucial role in your body. But you should be cautious about taking tryptophan supplements. Get immediate medical attention if you notice any side effects after starting a new product.