There are some persons with very sensitive stomachs that might experience stomach irritation directly after taking the supplement. Mixing with food will normally be able to prevent this. Also, please see our "How do I start taking my supplements" FAQ for examples of up-tapering schedules, designed to gradually bring your protocol to the full recommended dose over a period of time and minimize possible side effects.
Beyond that no major side effects have been noted, and all ingredients are classified under the FDA's GRAS (Generally regarded as Safe) category.