Tenormin (generic name: Atenolol) is a blood pressure medication. It's known as a beta blocker, and can treat high blood pressure (hypertension) as well as coronary heart disease and even some heart arrythmias. It works by widening the arteries and blood vessels, which lowers blood pressure and can help prevent heart attacks and stroke.

Tenormin was introduced in 1976 and made by pharmaceutical company AstraZenica. It offered many benefits over the previous best-seller, Inderal (Propanalol), because the latter had a tendency to cross the blood-brain barrier and be absorbed, causing depression as a side effect. Tenormin caused much less of that side effect (though in 2006 studies suggested it increased the risk of type-2 diabetes).

It's chemical formula is C14H22N2O3. (thanks wikipedia)

Nowadays, almost everyone uses the generic form of it; Atenolol. I haven't seen a brand-name prescription for it in years.