Which of the following supplements is NOT commonly associated with anxiolytic effects?

Vitamin C is primarily known for its immune-boosting properties and its role as an essential nutrient, rather than for any specific anxiolytic effects. While it can contribute to overall mental health by reducing oxidative stress and supporting brain function, studies have not demonstrated that it has direct anxiolytic properties.

In contrast, kava-kava, St. John’s wort, and valerian root are all supplements that have been traditionally used and studied for their potential to alleviate anxiety and promote relaxation. Kava is renowned for its calming effects and has been used to reduce anxiety in several cultures. St. John's wort is more commonly known for its antidepressant effects, but it can also have a positive impact on mood and mild anxiety. Valerian root is often used to promote sleep and relaxation, making it part of anxiety management strategies.

Thus, Vitamin C stands out as the supplement not typically associated with direct effects on anxiety, making it the correct answer in this context.