21.   The drugs may block the production of substances that are needed by the kidney.

22.   The drug blocks that protein.

23.   The drug blocks the conversion of testosterone into a chemical which is linked to prostate size, beard growth and, over time to male pattern baldness.

24.   The newer protease inhibitor drugs block a different enzyme.

25.   The protease inhibitor blocks a key viral enzyme called protease, and the older drugs block a different enzyme.

26.   These drugs block leukotrienes, substances that, like histamines, are released during inflammation.

27.   These drugs all block acetylcholine, a chemical secreted by nerves that tells muscles to contract.

28.   These drugs block the receptors in the brain that are involved in the brain reorganization which takes place during learning.

29.   TNF-alpha, the substance that the drug blocks, belongs to a class of substances known as cytokines.

30.   Other over-the-counter drugs block the production of acid.