Hlo, Hope you are doing great.

The basic eligibility for becoming drug inspector is that, you should possess a graduation in pharmacy or medicine along with it your age should be more than 18 years.
The work experience of 18 months is not essential but it depends upon the state too. Some states have a compulsion for work experience and while some do not  take this as mandatory. It depends upon the state in which you live and also sometimes the vacancies are also open for Freshers as well. So stay tune with the notification about vacancies also.

Hope it helps.
Best wishes