Dietary supplement use has increased during the past decade. Epidemiologic studies suggest that patients turn to dietary supplements because of a reluctance to take prescription medications or a lack of satisfaction with the results. They often perceive dietary supplements to be a safer or more natural alternative. Patients with mental health conditions, including depression, anxiety, and sleep disorders, are among those who use dietary supplements. St. John's Wort is used to treat depression. Clinical studies comparing dietary supplements with low-dose antidepressants (maprotiline, amitriptyline, or imipramine at 75 mg/day) or high-dose antidepressants (imipramine at 150 mg/day) find no significant difference between treatments. Kava kava is used to treat anxiety. Clinical trials demonstrate it to be superior to placebo, and roughly equivalent to oxazepam 15 mg/day or bromazepam 9 mg/day. Agents discussed for use in sleep disorders include melatonin, valerian, 5-hydroxytryptamine, catnip, chamomile, gotu kola, hops, L-tryptophan, lavender, passionflower, skullcap, and valerian. Familiarity with the evidence for use and the possible resulting risks can help health professionals to guide patient decisions regarding use of dietary supplements.