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.
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.
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.
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.
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.
Last updated and reviewed: 1 May 2019