Some experts believe a tryptophan deficiency can cause problems with sleep. Made from tryptophan, 5-HTP helps the body make serotonin. Low levels of serotonin are a known factor in sleepless nights. Taking a 5-HTP supplement may be a benefit if your body has low levels of tryptophan. How do you know if you're low? Low levels of tryptophan are most common in people who are depressed. If your insomnia is associated with depression, it might be a good question to ask your doctor. In one study, 100 mg of the supplement was enough to make sleep longer and better.