Now that’s a stiff penalty.

A former inmate who sued the city for making him suffer through a painful six-day erection was handed a $750,000 settlement on Monday.

The hefty payout amounts to $125,000 for each day of hard time served by Rodney Cotton, 51, who said he was treated “worse than a dog” at the Manhattan Detention Complex while enduring the uncomfortable side effect of an anti-depressant medication.

Cotton said the lack of medical attention rendered him impotent.

“It just started hurting,” Cotton told The Post Monday of his ordeal, which began on July 4, 2011, near the start of a 2½-year sentence for a parole violation. “And I’m like, what the hell is going on? It wasn’t going down.”

Cotton had asked to be taken to a jail clinic, but a guard at the facility, known as The Tombs, told him he’d have to wait until after the holiday weekend.

Desperate, Cotton faked chest pains to get a doctor to see him, only to be given ice packs and Tylenol.

Days later, he was finally taken to Bellevue, and underwent surgery to relieve the swelling. The doctors said the stitches would dissolve on their own. They didn’t, he claims.

The stitches had become embedded in the skin, and no anesthetic was used when they were being removed, Cotton said in his Manhattan Supreme Court suit.

Cotton said he still gets it on with the ladies, but he has to be more creative, and appeal to their sensitive side.

“I put up a facade,” he said. “There’s a young lady in the building who likes me. I’m scared to try anything with her. I take her out. I take her to Red Lobster. I take her to Outback. I do things for her son. But I don’t think I’m going to try having sex with her. It would be too embarrassing.”

Doctors said a lasting erection is a side effect of Risperdal, and a warning about it is listed on the website of the manufactuer, Janssen.

Cotton said he started taking Risperdal in 2003, the year after he finished a 12-year prison stint for manslaughter for killing a man during a 1989 fight over a sheepskin coat.

Now he’s going to take his money and move to Atlanta to be closer to his daughter.

“I can’t fix my situation, but I can soothe it,” he said.

A spokesman for the city’s Law Department, Nicholas Paolucci, said, “Settling this case was in the best interest of the city.”

In the meantime, the city has ended its contract with Corizon, the for-profit health care company that has drawn fire for the way it treated inmates such as Cotton.

Additional reporting by Leonard Greene and Reuven Fenton