My dermatologist's office had a special of buy two get one free, so I bought 3 boxes. It's about 4 weeks now, and I'm really happy with the lashes that are growing in.
To save some money, they recommended that I squeeze one drop into the little bottle cap, then apply the liquid with a soft little brush (I use a small watercolor brush, but an eyeliner brush will work as well). One drop is enough for both upper and both lower lashes, then I use what's left to touch up my inner and outer eyebrow thin spots. I'm not having any side efeects, and am usually pretty sensitive. It's just so cool to see the definition improve while using less and less mascara.