The drug fentanyl — which is up to 50 times stronger than heroin — is available in generic form. It is also a highly addictive street drug, manufactured in back-alley labs and laced in heroin to boost its potency. Fentanyl is used to treat extreme chronic pain that is unresponsive to other opioid pain relievers, such as breakthrough pain cancer patients often suffer. A fentanyl transdermal patch costs from $5 to $12 depending on the dose per hour. A 12 micrograms (mcg) per hour patch retails for about $5 and offers 72 hours of pain relief, whereas the 100 microgram per hour patch is about $12 with GoodRx coupon. Sounds like a bargain; pain-free bliss for $2 to $4 a day. That works out to about $50 to $125 per month.