5-hydroxytryptophan (5-HTP) is the precursor to the neurotransmitter serotonin. Side effects of 5-HTP can vary, but may include serotonin syndrome, gastrointestinal issues, heart and blood vessel issues, and more.

5-HTP is available as a supplement. Some older research suggests that it may help with mood issues, such as depression and anxiety, as well as headaches, chronic pain, and insomnia.

In this article, we explore what 5-HTP is and how it works. We also discuss the potential side effects of 5-HTP supplements.

5-HTP supplements next to a glass of water in shadow of water on flat surface.Share on Pinterest
Yulia Reznikov/Getty Images

Neurotransmitters are chemicals that help carry nerve signals between neurons. One example of a neurotransmitter is serotonin, which plays an important role in numerous bodily functions, including:

  • mood regulation
  • sleep
  • pain perception
  • digestion
  • blood clotting

The body needs an amino acid called tryptophan to make serotonin. The human body cannot make tryptophan, so a person must get it from the food they eat. Once the body receives this substance, it converts it to 5-HTP. It then turns the 5-HTP into serotonin.

5-HTP supplements are also available. Learn more.

Without tryptophan, the body cannot make serotonin. The National Capital Poison Center notes that tryptophan was available in the form of supplements until the Food and Drug Administration (FDA) banned them in 1989.

The ban came into place after a contaminated batch of tryptophan caused the deaths of at least 30 individuals and made more than 1,500 people very sick.

As 5-HTP is a precursor to serotonin, it is a suitable alternative to tryptophan supplements. 5-HTP supplements may help raise serotonin levels, especially in people who do not get enough tryptophan from their diets and those whose body does not make enough serotonin.

Research suggests that 5-HTP is highly absorbable. An older review from 1998 notes that the body absorbs about 70% of an oral 5-HTP supplement into the bloodstream.

The potential risks and side effects of 5-HTP vary among children, adults, and people who are pregnant or breastfeeding.

In children

According to health experts, 5-HTP is not safe for children.

In adults

The possible side effects of 5-HTP in adults include the below.

Serotonin syndrome

Serotonin syndrome is a life threatening emergency that occurs when a person has dangerously high levels of serotonin in their brain. Symptoms of serotonin syndrome may include:

Serotonin syndrome usually occurs as a result of taking multiple serotonin-producing drugs. For example, a person may develop the condition after taking a selective serotonin reuptake inhibitor or a serotonin and norepinephrine reuptake inhibitor with one of the following:

Due to this risk, individuals who take antidepressants or other serotonin drugs should not take 5-HTP.

Gastrointestinal issues

Some people report the following gastrointestinal symptoms after taking 5-HTP:

  • heartburn
  • gas
  • rumbling sensations in the stomach
  • feelings of uncomfortable fullness

Heart and blood vessel issues

Serotonin causes tiny blood vessels to narrow, which helps promote blood clotting. And while this narrowing can help stop bleeding after an injury, it may increase the risk of dangerous blood clots in some people.

Individuals with a history of high blood pressure or other cardiovascular risk factors should speak with a doctor before taking 5-HTP.


Very high levels of serotonin in the blood may lead to osteoporosis, where the bones weaken, especially in people with other risk factors for the condition.

Those with osteoporosis often do not experience any symptoms — the first sign is usually a broken bone following a minor fall or another injury.

A person who already has an osteoporosis diagnosis should talk to their doctor before taking 5-HTP.

Eosinophilia-myalgia syndrome

Eosinophilia-myalgia syndrome (EMS) is a rare disease that causes elevated levels of white blood cells called eosinophil in the body’s tissues. These raised levels can lead to the following symptoms:

Severe cases of EMS can lead to multiple organ failure and death. EMS is the syndrome that led to the deaths of at least 30 people who took tryptophan supplements in 1989.

A few individuals who have taken 5-HTP have since reported symptoms of EMS.

Overdose and toxicity

Higher doses of 5-HTP increase the risk of serious side effects, including overdose and organ failure.

The FDA does not regulate supplements, meaning there may be significant differences in content and quality among batches and brands. This inconsistency increases the risk of overdose and poisoning.

Allergic reaction

As with any supplement, it is possible to have an allergic reaction to 5-HTP, while severe allergic reactions are possible but rare.

Anyone who experiences symptoms of a severe allergic reaction, or anaphylaxis, after taking 5-HTP should seek emergency medical attention. These symptoms may include:

  • skin rash or hives
  • swelling of the lips, tongue, or throat
  • shortness of breath or difficulty breathing
  • stomach pain
  • abdominal cramps
  • vomiting or diarrhea
  • a feeling of impending doom

During pregnancy and breastfeeding

Scientists have not sufficiently evaluated the safety of using 5-HTP when pregnant or breastfeeding. As a result, people who are pregnant or breastfeeding should avoid taking this supplement.

5-HTP may interact with any drug that increases serotonin, including:

People who take any of the above drugs should not take 5-HTP — doing so can potentially cause serotonin syndrome.

As a general rule, individuals should always consult with a doctor before taking a supplement for the first time.

There is no FDA-approved dosage of 5-HTP. An overdose could be lethal, so it is important to begin with a small dose and avoid taking more than the product label recommends.

A person should talk with their doctor before taking a new supplement, as some supplements can worsen existing health conditions or interact with other medications. A healthcare professional may also be able to advise on an appropriate supplement dosage.

After taking 5-HTP, an individual should contact a doctor if:

  • the 5-HTP does not improve their symptoms
  • they develop new or worsening symptoms while taking 5-HTP
  • they experience unpleasant side effects

A person needs emergency medical attention if anaphylaxis or signs of serotonin syndrome occur after taking 5-HTP.

The supplement 5-HTP may help boost levels of the neurotransmitter serotonin. Some older research suggests it may help regulate mood and alleviate headaches, chronic pain, and insomnia. However, further research is necessary to support these claims.

Additionally, 5-HTP may cause side effects in some people. Possible severe side effects include serotonin syndrome and anaphylaxis. Anyone who experiences symptoms of these side effects should seek emergency medical attention.

A person should talk with their doctor before taking 5-HTP or any other supplements. Some supplements can worsen underlying medical conditions or interact with medications they are already taking.