Are there any libido enhancers that have been shown to work?

Not really: No otc male enhancement medications have been clinically shown to improve libido. Often, they rely on placebo effect.

Prescribed testoster: Certainly there are many prescriptions such as testosterone to treat low testosterone; viagra (sildenafil) apparently increases libido in women but these medications are not without risks and should not be prescribed prior to a full evaluation by a physician.