11.   A spokeswoman for the Food and Drug Administration said there was no guarantee of exclusivity when drugs that have lost their patent protection become available without a prescription.

12.   Aaron of the Brookings Institution said the pressure to add prescription benefits to Medicare would increase as more and better drugs became available from pharmaceutical companies.

13.   Add a blue-ribbon panel charged with reforming Medicare, and prescription drugs becomes an irresistible subject.

14.   Addiction has become common in Iran, where drugs have become cheap and easily obtained.

15.   But anecdotal evidence from casual users of marijuana suggests at least that drug has become scarcer and more expensive in New York and Boston.

16.   But he said he was relieved to learn that similar but less risky drugs had become available.

17.   But the drug soon became the subject of controversy and complaints.

18.   But the drug has also become more dangerous for new users.

19.   By contrast, tumors often become resistant -- that is, the drugs become ineffective -- when conventional chemotherapy agents that had originally been effective are administered again.

20.   Consequently, drugs may simply become impotent, and the unsuspecting user may increase the dosage to get results.