Pretty hard, at least right now. There is a shortage of mental health professionals in general, including substance abuse counselors, but this is because of a funding shortage, not a shortage of people wanting to work in the field.
Usually you need a masters degree, in either social work, counseling, or psychology. With any of those degrees you are eligible to get a license in that profession and a separate substance counseling certification depending on the state.
The field has also been notoriously saturated with people in recovery themselves, but many places are pushing away from this. Instead there is a push for peer supports. So if you happen to be in recovery there is a special certification, again depending by state, usually called CRS Certified Recovery Specialist, so you can pretty much work as a counselor without the degree. But don't expect to see many masters level counselor or peer support positions until there is more $$ out there to pay for it.