No side effects. Better than taking same medicines orally.
Severe cough means it's an exacerbation. He will need additional oral anti inflammatory (steroids) along with Salamol inhaler to recover.
Next Steps
If you wait for cough to get too severe, air passage would get too narrow and no medicine would go in.
Health Tips
To prevent such severe cough, there are 'preventer' medications, also as inhaler, that may have to be used for some time