Side effects associated with 5-HTP are rare but may include headaches, mild stomachaches, nausea, nasal congestion, and constipation. There are anecdotal reports that taking high doses of 5-HTP causes nightmares or vivid dreams. Side effects may be minimized by starting with a low dose of 5-HTP and taking it with food.
It is theorized that the effectiveness of 5-HTP may be enhanced by taking vitamin B6 and niacinamide. The action of 5-HTP may be enhanced by extracts of ginger, passionflower (Passiflora incarnata), St. John's wort, and Ginkgo biloba.
Dopa-decarbolylase inhibitors, such as carbidopa or benserazide block the enzyme that is responsible for the destruction of dopamine. However, a study by the Massachusetts College of Pharmacy and Health Sciences demonstrated that 5-HTP reaches the brain without the use of a dopa-decarboxylase inhibitor, and will produce the benefits of stress reduction and reduced food intake even when used alone.