Tryptophan is an essential amino acid used to make proteins. Your body does not make it, so you need to get it from your diet. Foods that contain tryptophan include animal products like chicken and fish and plant foods like nuts or soy.

After we eat tryptophan, the body converts some to 5-HTP and then into the neurotransmitter serotonin. The body also converts some tryptophan to nicotinamide adenine dinucleotide (NAD), which is why tryptophan is also considered a dietary source of niacin.

There are two types of tryptophan: L-tryptophan and D-tryptophan. The only difference between the two types is the orientation of the molecule.

You can get tryptophan through certain foods or a supplement in powder form.

Tryptophan can be found in some foods, especially those high in protein. Foods known to be high in tryptophan include:

  • chicken
  • eggs
  • cheese
  • fish
  • peanuts
  • pumpkin and sesame seeds
  • milk
  • turkey
  • tofu and soy

In order for tryptophan to be converted into niacin, however, your body needs to have enough iron, vitamin B6, and vitamin B2.

Tryptophan can have plenty of health benefits, but the supplement can cause a number of unpleasant side effects in people.

The most common are gastrointestinal side effects, which include:

Other common side effects include:

More serious side effects, which warrant immediately stopping consumption, include:

There are a number of health benefits from the naturally occurring tryptophan found in foods. Most of these health benefits come from the potential increase of niacin and thus serotonin. The benefits from more serotonin include:

While tryptophan consumed through food is typically safe, some people experience adverse effects from the supplement form.

According to the National Organization for Rare Disorders, tryptophan supplements were linked to over 1,500 reports of eosinophilia-myalgia syndrome (EMS) and 37 deaths in an epidemic in the late 1980s.

This is a rare disorder that affects multiple organ systems within the body, including the skin, lungs, and muscles. It’s often sudden and progresses rapidly. It can be disabling and it can even cause death. Symptoms include:

  • muscle pain or weakness
  • skin rashes
  • cramping
  • difficulty breathing
  • fatigue

However, the EMS cases were traced back to a manufacturer whose tryptophan supplements were tainted. Because of this, the medical problems were likely due to contamination of the supplements rather than tryptophan itself.

Tryptophan can help treat symptoms of some conditions, but it may raise your serotonin levels too much, especially if combined with medications like:

If you’re taking selective serotonin reuptake inhibitors (SSRIs), you shouldn’t increase your tryptophan without talking to your doctor.

The increased serotonin from the tryptophan can contradict the purpose of the SSRIs. Several common depression medications fall under this category, including:

As it’s best to err on the side of caution, avoid taking tryptophan if you’re pregnant, trying to become pregnant, or breastfeeding.

Tryptophan is commonly used to treat insomnia and sleep disorders like sleep apnea. However, there’s not enough evidence to determine whether this is an effective use. More research needs to be done to see if tryptophan is safe to treat any of these conditions.

Tryptophan has been noted as possibly effective for helping to relieve premenstrual dysphoric disorder (PMDD). Some older research shows that tryptophan may be effective for smoking cessation, too.

While tryptophan supplements are available, they may have side effects for some people. Because of this, it may be safer to obtain tryptophan through the foods that naturally contain it, like meat, fish, and cheese.

Instead of tryptophan supplements, your doctor may recommend that you take 5-HTP supplements instead, which is tryptophan before it’s fully converted into serotonin.

If you do decide to take either supplement, talk with your doctor first to make sure that it’s safe for you.