Pfizer’s smoking-cessation drug Chantix nudged closer to blockbuster status last year, bringing in $997 million in sales—up 18% from 2016. But some portion of that may have come from price hikes, judging from a new report released by GoodRx, an aggregator of pricing and discount information on prescription drugs.

The price of a 30-day supply of Chantix has more than doubled to $485 since 2013, according to GoodRx. Sure, a big proportion of patients do get help paying for the drug from their health plans, but that assistance may not be so generous: Many insurers have relegated the drug to tier 3 status on their formularies, putting patients on the hook for high out-of-pocket costs, GoodRx reports.

"Chantix’s soaring price, coupled with its poor coverage, does not bode well for the estimated 37.8 million Americans who are currently smoking," wrote GoodRx researcher Tori Marsh in a blog post. "Moreover, tobacco use disproportionally affects low-income populations—those that may not be able to afford to pay for Chantix." Marsh told FiercePharma that the pricing information came from a "representative sample of U.S. prescription fills," based on full list prices from pharmacies.

A spokeswoman for Pfizer said in an email to FiercePharma that the prices patients pay for prescriptions are "ultimately set by insurers" and that Chantix is covered by many insurance plans for a low or zero copay. "We recognize not all patients have health insurance or adequate prescription coverage and any eligible patient who cannot afford Chantix may receive the medicine for free or at a reduced price through our patient assistance programs," she added.

Chantix has had an up-and-down ride since it was approved in 2006. The consensus is that the drug works wonders for many people trying to kick the habit—Pfizer has reported that 44% of patients quit after 12 weeks on the drug—but side effects have been a point of contention. When reports emerged of suicidal thoughts, nightmares and other psychiatric side effects suffered by patients taking the drug, the FDA slapped a black box warning on it in 2009. It wasn’t until late 2016 that the company finally persuaded the agency to remove the warning.

In 2013, the company laid out $273 million to settle a majority of the 2,700 state and federal lawsuits that had been filed over alleged side effects. In addition to concerns about psychiatric effects, the FDA has noted that the drug may raise the risk of heart attacks. All of this has made it that much harder for Pfizer to live up to early predictions that Chantix would be a blockbuster.

Pfizer continues to take heat for its pricing practices, and not just on Chantix. In January, Wells Fargo released a report revealing that the company pushed through 116 price hikes in 2017 ranging from 3% to 9.46%. Pfizer has also come under fire in the U.K., where that country’s Competition and Markets Authority tried to fine it $112 million for its alleged role in a 2,600% price hike on epilepsy drug Epanutin. Pfizer appealed the decision and prevailed earlier this month.

High drug prices remain a hot-button issue in Washington. FDA chief Scott Gottlieb, M.D., is chipping in by easing the path to approval for generic drugmakers and calling out pharma companies that try to stifle the development of low-cost copycats. More recently, HHS Secretary Alex Azar suggested getting rid of drug rebates that pharma companies dish out to pharmacy benefit managers and other payers. Azar is testifying on the drug-price issue before the Senate Finance Committee on Tuesday.

Meanwhile, Pfizer is supporting ongoing efforts to grow the market for Chantix, with mixed results. In March, the company announced that in a phase 4 study in smokers age 12 to 19, Chantix did not outperform a placebo in achieving four weeks of continuous abstinence. The study was required by U.S. and European regulators, and Pfizer is planning to submit the data to regulators in a bid to gain pediatric exclusivity for the drug.

Editor's note: This story has been updated with a response from Pfizer.