The information which you have given is not sufficient because mg depends upon mass and so many other factors.
 
but if its liquid like medicine then according to doctors 12.5 mg is one teaspoon
 
1 mg = 1/12.5 teaspoons
 
therefore
 
55 mg = 55 (1/12.5) = 4.4 teaspoons
 
approximatley 4 and a half teaspoons. 

 In fluid measures, 1 teaspoon = 5 mls (millilitres) i think this is probably what you are looking for. So that would be 11 teaspoons.