Phenylalanine

L-Phenylalanine is converted into tyrosine.
L-Phenylalanine, especially when combined with UV light, is used to treat vitiligo, a condition causing white patches on the skin. It seems to work by boosting melanin production, helping repigment the skin, with studies showing benefits in over 90% of early cases.
D-Phenylalanine may interact with the niacin receptor 2.
DL-Phenylalanine is noted for potential pain relief, possibly by preventing the breakdown of enkephalins, the body's natural painkillers, and may also have antidepressant properties.
It is converted to tyrosine by the enzyme phenylalanine hydroxylase.
DL-Phenylalanine is a mixture of L- and D-forms.
High levels of phenylalanine can be neurotoxic, particularly in phenylketonuria (PKU), a genetic disorder where individuals cannot metabolize phenylalanine properly. Chronic high serum levels can lead to seizures, organ damage, intellectual disability, and behavioral issues like ADHD (Phenylalanine | C9H11NO2 | CID 6140 - PubChem).
For PKU, early dietary restriction and medication are recommended to manage levels, with D-Phenylalanine potentially arresting fibril formation by L-Phenylalanine, suggesting a therapeutic role (Phenylalanine | C9H11NO2 | CID 6140 - PubChem).
For instance, a study on energy intake showed that high doses (10 g) increased nausea ratings in overweight/obese women, with no significant effect on energy intake compared to controls (Phenylalanine | C9H11NO2 | CID 6140 - PubChem).

Form	Pharmacological Action	Details
L-Phenylalanine	Precursor to neurotransmitters	Converts to tyrosine, then dopamine, norepinephrine, epinephrine; affects mood, cognition.
L-Phenylalanine	Treatment for vitiligo	Combined with UV light, stimulates melanin production; effective in early cases.
D-Phenylalanine	Activity at niacin receptor 2	Interacts with niacin receptor 2; specific effects unclear.
DL-Phenylalanine	Analgesic effects	Inhibits enkephalin degradation, potentially relieving chronic pain.
DL-Phenylalanine	Potential antidepressant effects	May enhance neurotransmitter levels; evidence mixed.