This mental health survey may not be so good for the city’s fiscal well-being.

The city shelled out $8.8 million in taxpayer money to produce and send out mental-health questionnaires that contained $5 bills as an incentive for filling out the forms — but many likely wound up in the trash because the envelopes looked like junk mail, galled critics told The Post.

The Health Department, working with the City University of New York, sent the surveys to 210,462 households in early May with a goal of netting 50,000 responses — but only 12,759, or an abysmal 6%, replied as of June 27.

“They’re taking a gamble that [even] 10% of people will open it. That’s bananas!” Jennifer Crocker, 37, who happened to open her mailer, told The Post.

“The city is throwing away our money.”

Since May 11, plain white envelopes bearing only the Health Department’s logo — and a note on the outside that people can earn $20 — have been mailed out. Inside is the cash, the roughly 60-question survey, and a letter from Health Commissioner Dr. Ashwin Vasan explaining how participants’ personal information could assist the city in determining “helpful resources for you and your loved ones.”

“Over the past few years, we have faced significant changes in our lives,” the letter reads, inviting respondents to “participate in a voluntary, 15-minute survey on changes affecting your community.”

“We have attached $5 to this letter as our way of thanking you” in advance for participating in the survey, it adds, promising an additional $20 reward to each household that completes the questionnaire. 

Some of the questions asked about people’s prescription and recreational drug use in the past year, as well as whether they had support if they were feeling down, survey participants said.

Research firm Ipsos was paid $7.5 million to conduct the survey, according to Monique Williams, project manager at the CUNY Institute for Implementation Science in Population Health.

Critics said the no-strings-attached cash was short-sighted — especially since the city is expected to face an $4.2 billion budget shortfall by 2025, according a Comptroller’s report issued last month.    

“With all the mail theft and spam we’re dealing with, I can’t help but wonder if people just tossed the survey and the $5 — or thieves ended up with more money in their pockets,” said City Councilman Robert Holden (D-Queens).

“There are better ways to gather opinions without cash incentives that could end up in the trash or stolen. With the city facing a financial cliff, we need to spend taxpayer dollars wisely, and this survey was dumb.”

Rachel Vick, a Health Department spokesperson, said that getting a leg-up in hearing from New Yorkers about their health and wellness was worth it. 

“Due to the high value the city places on hearing directly from as many people as possible, we have utilized a modest incentive for survey participation,” Vick said.

“This incentive strategy is a long-utilized, evidence based strategy for robust data collection.”