python: unhashable type error

counter[row[11]]+=1

You don't show what data is, but apparently when you loop through its rows, row[11] is turning out to be a list. Lists are mutable objects which means they cannot be used as dictionary keys. Trying to use row[11] as a key causes the defaultdict to complain that it is a mutable, i.e. unhashable, object.

The easiest fix is to change row[11] from a list to a tuple. Either by doing

counter[tuple(row[11])] += 1

or by fixing it in the caller before data is passed to medications_minimum3. A tuple simply an immutable list, so it behaves exactly like a list does except you cannot change it once it is created.

As Jim Garrison said in the comment, no obvious reason why you'd make a one-element list out of drug.upper() (which implies drug is a string).

But that's not your error, as your function medications_minimum3() doesn't even use the second argument (something you should fix).

TypeError: unhashable type: 'list' usually means that you are trying to use a list as a hash argument (like for accessing a dictionary). I'd look for the error in counter[row[11]]+=1 -- are you sure that row[11] is of the right type? Sounds to me it might be a list.

I don't think converting to a tuple is the right answer. You need go and look at where you are calling the function and make sure that c is a list of list of strings, or whatever you designed this function to work with

For example you might get this error if you passed [c] to the function instead of c