Btw
"The appropriate category of product (medical device, drug or biologic) is determined by the primary mode of action of the product. Follica’s lead product candidate operates primarily by its TCP device.
Drugs already in receipt of FDA approval will be used in conjunction with Follica’s TCP device without change to their route of delivery or indication. Therefore, Follica’s lead product candidate is anticipated to be regulated as a medical device. Assuming a successful read-out of its next clinical study
(i.e. after demonstrating that Follica’s lead product candidate can stimulate cosmetically significant hair growth through TCP and at-home application of an approved drug) Follica expects to seek regulatory approval in the US in late 2017."
It's very simple they go for 510K approval and the drug(s) used will be drug(s) that are already on the market.
Two very logical compounds are minoxidil and PGF2a (latanoprost) to me as both are off-patent and the strongest hair growth modulators.
I'm actually almost certain that it's minoxidil though since they mention there is no change of route of delivery or indication (FDA dodge obviously

).
That's not to say that they eventually might research novel compounds but as we know that will take many many years, because new drug applications will go need through the FDA loop and the painstaking costly long process.
@occulus