Dynamic nested form in Rails

I have a Rails 3.2.22 app that I'm maintaining and I need to create a quasi-complex form. It's a form that records medications into a report.

So my thought is to build a model called NarcoticUsage to contain the record then an associated/nested Model called Narcotic which will be the actual model with the drug names.

I need to somehow within the Narcotic usage form include functionality to add multiple instances of the Narcotic model. ie. A form where you would have the drug name (from Narcotic model), then the expiration date and serial numbers of the drugs (stored in NarcoticUsage). In the form I'd like to be able to click a "+" sign or something like that to add multiple drugs. So in essence if someone recorded Tylenol, Cough Syrup, Ativan they could add a dynamic field to fill in the drug name (from narcotic), then enter the expiration date and serial numbers associated with the narcoticusage model.

I have some ideas on how to design the models and forms using nested_attributes but I'm not sure the best way to design this is.

Any thoughts on best practices with nested_forms?

Thanks in advance and if you need clarification or some sample code, please let me know.