For a powerful new pill that's supposed to ease pain, Zohydro is causing major headaches for an increasingly vocal group of critics.

Zohydro is a potent extended-release formulation of hydrocodone, an opiate painkiller that's been in use for decades and the primary analgesic ingredient in drugs like Vicodin.

However, unlike other formulations of hydrocodone, Zohydro is uniquely free of added medications like aspirin (as in Azdone and Lortab ASA), ibuprofen (Vicoprofen), or acetaminophen (Vicodin and Norco). That means that Zohydro can be prescribed as stand-alone hydrocodone -- free from worry about aspirin allergy and side effects, ibuprofen kidney and GI toxicities or acetaminophen overdose and liver damage.

This improved patient safety profile is what makes Zohydro an appealing alternative to traditional hydrocodone-combination drugs. Additionally, because Zohydro is engineered in an extended-release form, it need be given only twice a day -- a convenience for patients who require chronic opiate therapy.

And yet these same selling points are cited by critics in advancing arguments against Zohydro's release. That's because with Zohydro, if you're not forced to take a dose of acetaminophen or aspirin every time you swallow a hydrocodone tablet, the amount of hydrocodone you can take is no longer limited by side effects from acetaminophen or aspirin.

Critics insist that will encourage excess intake of hydrocodone, worsen the epidemic of opiate-drug abuse, and lead to higher death rates from overdose. They've petitioned the FDA to withdraw its approval of Zohydro, and bills have been filed in the House and Senate to remove Zohydro from the market.

There's great merit on both sides of the Zohydro debate. When matched milligram-for-milligram of hydrocodone, Zohydro offers patients and doctors a better safety profile, but it is likely to become yet another drug of social abuse.

Dr. Robert V. Brody, chief of the Pain Consultation Clinic at San Francisco General Hospital, views the debate as a longer-standing national narrative about our approach to treating chronic pain. He reminds us that, initially, doctors tended to reserve chronic opioid therapy for cancer patients or people dying in pain. After witnessing how that could "help such patients function in their lives," we began using chronic opioid therapy to help patients with chronic noncancer pain as well.

But our rising use of prescription opiates has rubbed up against various sociopolitical attempts to rid society of illicit opiates like heroin, as it has also spurred initiatives within the medical community to limit opioid prescribing. These parallel trends created markets for illicit drug use that alternatively favored prescription opiates like OxyContin or illegal ones like heroin -- depending on what's more available and less expensive.

Brody hopes that while addressing our serious national drug problem, we don't shy away from treating individual patients in chronic pain. But he is worried that already "we may be moving backwards" in that regard, and he points to mounting difficulties in finding primary care doctors who are willing to prescribe chronic opiates.

While Brody considers Zohydro a "great tool that will help some people function in their lives," he thinks its use should not be dictated by the U.S. Senate. He also says it would have been preferable had Zohydro been manufactured in a non-crushable form to limit its potential for illicit use and abuse.

Dr. Amy Haddad, co-author with Dr. Robert Veatch of "Case Studies in Pharmacy Ethics" and director of Creighton University's Center for Health Policy and Ethics, shares concerns about Zohydro's physical formulation.

In an email interview, she underscored the troubling "potential for lethal harm" from the rapid release of massive opiate doses if Zohydro were chewed or crushed.

She emphasized that while much attention was being focused on illicit users, the potential for such lethal harm applied "as well for 'legitimate' users ... ."

Haddad reasoned that to justify such a serious risk, "one would have to argue that the need of chronic pain patients is so great that we are willing to accept that risk" and unable to wait for the drug's manufacturer (Zogenix, Inc.) to produce a safer formulation. But she didn't think that to be true.

Meanwhile, the debate over Zohydro has been muddled by curious political and regulatory activities. For example, it remains unclear why the FDA decided to approve Zohydro against the advice of its own advisory panel, or why FDA regulators did not require a formulation of Zohydro with less potential for harm and abuse.

And we still await investigation of serious "pay-to-play" allegations that private meetings between drug companies and federal regulators may have influenced Zohydro's approval.

It will be particularly interesting to see what happens with the Senate bill aiming to force Zohydro off the market. That's because its major proponent, Sen. Joe Manchin, D-W.Va., has received significant campaign contributions from Mylan Pharmaceuticals -- a company that manufactures several opioid drugs including oxycodone, extended-release morphine, and even hydrocodone-acetaminophen tablets.

Additionally, sales of these products could suffer in competition with Zohydro. And that would be undesirable for Mylan and its CEO -- who just happens to be Manchin's daughter.

Kate Scannell is a Bay Area physician and the author most recently of "Flood Stage."