Merck & Co. says the Food and Drug Administration has approved its new tablet for grass allergies, Grastek, for patients five to 65 years old.

Meant as an alternative to weekly allergy shots, the tablet dissolves under the tongue. Taken daily for a few years, it gradually reduces sensitivity to common grasses, instead of temporarily relieving symptoms including sneezing, runny nose, and itchy, watery eyes.

Merck, based in Whitehouse Station, N.J., will market the in North America. Its partner, ALK-Abello, sells it in Europe as Grazas.

Merck said Grastek will be available in U.S. pharmacies in late April. However, it's best to start taking it three months before grass pollen season begins.

The drug can cause severe allergic reactions and shouldn't be used by patients with severe asthma.