Phenylalanine comes in several forms as a supplement:
L-phenylalanine is an essential amino acid. It's also found in protein in the foods we eat.
DL-phenylalanine, which contains both the D- and L-forms
As a supplement, some people use NAC to try to protect the liver. There's evidence it can help prevent liver damage caused by some cancer drugs.
Some animal studies have shown that NAC may help protect against some cancers. However, there is little evidence that it would have anti-cancer benefits in people.
There's mixed evidence about whether NAC helps with other conditions, like infertility, the flu, cystic fibrosis, liver disease, angina, HIV, and some eye conditions. More research is needed.
Optimal doses of NAC as a supplement have not been set for any condition. Quality and active ingredients in supplements may vary widely from maker to maker. This makes it very hard to set a standard dose.
There are standard doses for prescription uses of NAC. These depend on the condition that is being treated. Ask your doctor for advice.
Can you get NAC naturally from foods?
NAC cannot be found in foods.
What are the risks?
Tell your doctor about any supplements you're taking, even if they're natural. That way, your doctor can check on any potential side effects or interactions with medications.
Side effects. NAC may cause:
Risks. Extremely high doses -- 60 to 100 times the normal amount -- have caused liver damage in animals. NAC may not be safe for people with asthma or with severe liver or kidney disease.
Interactions. If you take any medicines regularly, talk to your doctor before you start using NAC supplements. They could interact with nitroglycerin or other medications.
The U.S. Food and Drug Administration (FDA) does regulate dietary supplements; however, it treats them like foods rather than medications. Unlike drug manufacturers, the makers of supplements don’t have to show their products are safe or effective before selling them on the market.