I would not merge the Drugs glossary and your regular glossary.
Rather include the Drugs in your regular glossary, and if you add a new drug, always add it to the Drugs glossary. The next time you open Instant Text it will be updated in your regular glossary.
This is useful when you start using different glossaries for different doctors or specialties. You only add the drug into Drugs glossary once, and it will be updated in all the glossaries where it may be included.
Same for the converted DocQscribe glossary. Just use the Includes button in the Glossary Viewer to include it to your regular glossary.