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Question mark: This treatment has not been properly researched. It is not possible to say whether they are useful or not.


The rating system

  • 3 smiliesThese treatments are very useful. They are strongly supported as effective by scientific evidence.
  • 2 smiliesThese treatments are useful. They are supported by scientific evidence as effective, but the evidence is not as strong.
  • 1 smileyThese treatments are promising and may be useful. They have some evidence to support them, but more evidence is needed to be sure they work.
  • No smiley On the available evidence, these treatments do not seem to be effective.
  • Question markThese treatments have not been properly researched. It is not possible to say whether they are useful or not.
  • Exclamation MarkSafety or other concerns have been raised for the use of these treatments.

What is it?

Phenylalanine is an amino acid. It is not made naturally in the body. Protein-rich foods such as meat, fish, eggs, cheese and milk are all a source of L-phenylalanine and other amino acids. D-phenylalanine is a man-made kind of phenylalanine, and DL-phenylalanine is a combination of the D and L forms.

How does it work?

Phenylalanine is converted to another amino acid in the body, which then produces chemical messengers in the brain (e.g. dopamine and norepinephrine). It is thought that these chemical messengers help regulate how we cope with stress and may impact mood.

Is it effective?

There is very little scientific evidence on phenylalanine for the treatment of depression. More studies of better quality are needed.

A 1979 study tested the effectiveness of DL-phenylalanine compared to an anti-depressant drug. Phenylalanine was as effective as the anti-depressant, however the study had no control group and it had a very small number of participants.

There have been no recent scientific studies on the use of phenylalanine for depression.

Are there any disadvantages?

People should not take phenylalanine if they have the genetic disorder phenylketonuria or if they are pregnant.

Dietary supplements, including phenylalanine, may have negative interactions with prescribed medications or other supplements, and could have side-effects. They should always be taken under the supervision of a health care professional.

Where do you get it?

Phenylalanine is found in many protein-rich foods such as meat, eggs and cheese. Phenylalanine supplements are available at some pharmacies and supplement stores.


There is not enough evidence at this stage to recommend phenylalanine as a treatment for depression.

Key references

  • Beckmann H, Athen D, Olteanu M, Zimmer R. DL-phenylalanine versus imipramine: a double-blind study. Archiv fur Psychiatrie und Nervenkrankheiten 1979; 227: 49-58.

Last updated and reviewed: 11 August 2023