Strategy-design of a database for medication
I would suggest you merge the 1st 2 tables, since every box will contain a single type of medicine. This way querying your database would be faster as well. 

Eg. You want to get the qty of medicines of a particular type, you will have to query by joining these 3 tables. Instead, add the medicine name column in the second table and for medicines with no stock you can get the data from a single table, instead of querying 2 tables.