Surprisingly, it does work for some cats:

With any new behavioral problem, first take your cat for a thorough medical evaluation. Next, assess litter type and litter box size, placement, location, and number to see if changes there might solve the problem. You can also try other behavior modifications such as pheromones. If you are still unable to prevent your cat from engaging in inappropriate elimination, you are dealing with what is called a “learned aversion.” This means that although there may be nothing wrong with the litter box situation, your cat has come to associate elimination in the litter box with negative experiences, be it pain or other types of stressors. In order to circumnavigate this learned aversion, anxiolytics (medications which decrease anxiety, such as Prozac) can help immensely.

Currently, fluoxetine (the drug name for the trade name Prozac) is available on the veterinary market for use with dogs to help manage separation anxiety (under the brand name Reconcile) and veterinarians have begun using this drug to manage feline elimination problems as well. This drug can be used for a range of cat behavior issues, from urine spraying to defecating outside the box.

Fluoxetine increases serotonin levels in the central nervous system. Serotonin is a neurotransmitter involved in facilitating social interactions, coping mechanisms, and adaptability. Absorbed extremely well orally, this drug is administered to cats most commonly in pill form. This medication is also available through compounding pharmacies as a transdermal application.

It usually takes a few weeks to a month on this medication before an owner begins to see corrections in litter box behavior, since the onset of this drug’s action can be slow. Some cats can gradually be weaned off the drug after four to six months. Others seem to need to be on it for the remainder of their lives.

Works for my cat, but it also shuts him up & makes him less attentive. Then I miss his raspy "Meowww"

How long have you been giving them to him? Do you ever not give it to him?

A couple years & yes I give him breaks from it so he can just be a cat until he pees again & it works immediately not weeks or months as stated. 

And sometimes those breaks can last a couple months

Well that's cool that he takes breaks. And uncool that he uses them to be a bad kitty.

ASPCA says kitty prozac can help with general timidity, litterbox problems caused by anxiety, urine marking, aggression, and compulsive behavior such as obsessive grooming:

http://www.aspca.org/pet-care/virtual-pet-behaviorist/cat-behavior/behavioral-medications-cats

You can buy 30 10-mg tablets for $27: http://www.1800petmeds.com/Fluoxetine-prod10489.html

Good description:

Fluoxetine is an antidepressant in a group of drugs called selective serotonin reuptake inhibitors (SSRI's). Fluoxetine affects chemicals in the brain that cause depression, panic, anxiety, or obsession-compulsion. Fluoxetine is a prescription medication used in dogs and cats for the treatment of canine aggression and obsessive-compulsive disorder. Fluoxetine is available as 10mg tablets and 20mg capsules. The usual dose is dependant on the condition being treated and the animal's response to treatment. It may take up to 3 or 4 weeks before the medication becomes effective.

Time magazine has an anecdote:

http://content.time.com/time/magazine/article/0,9171,2029480,00.html

Relevant part:

Sara, a former shelter cat, has been luxuriating in my home for nine years. She's always been gentle yet skittish, the proverbial scaredy-cat. But after Sammy—a high-spirited (read: aggressive) 5-year-old rescued by the ASPCA—moved in with us two months ago, it was all-out feline war. Sara hissed, Sammy pounced, and I couldn't get much sleep. Desperate to end the territorial battle before my apartment got destroyed—or, worse, marked with urine—I decided to consult my fabulous (but fabulously expensive) veterinarian. I left her office with two pheromone collars, a handful of pheromone diffusers and the ardent hope that the chemical compounds would bring peace to the Sachs household.

I'm not the only pet owner who has sought such relief. According to veterinary experts, behavioral problems are one of the leading reasons that animals are given away or euthanized. With the number of pet cats in the U.S. soaring 18% in the past decade, to 86 million, and with 56% of owners taking in more than one cat, it's no wonder that so many vets are prescribing low doses of fluoxetine (generic Prozac) to calm ruffled felines.

...

Research indicates that synthetic feline pheromones really do have a calming effect on cats—like a kitty Prozac but without the pill. Numerous studies, in journals such as Veterinary Record and Applied Animal Behaviour Science, have found that Ceva Animal Health's Feliway pheromone sprays and diffusers help reduce stress-related behaviors such as urine marking, vertical scratching and aggression.

Over the past year, more than a million cat-owning households have used pheromone products, which have no effect on humans or other noncat species. Ceva's Feliway diffusers, which look a little like plug-in air fresheners, have been available for more than a decade. Flea-collar maker Sergeant's started selling Sentry Good Behavior pheromone collars in April 2009. Both are cheaper than a vet visit. The diffusers cost $48, while the collars sell for $12 to $15. Results can be seen quickly, typically within a few days. The drawback: these products may need to be replaced after 30 days, so long-term use can get pricey.

Although each of the two manufacturers uses a different patented pheromone, there is no catfighting between them. To the contrary, says Larry Nouvel, a chemist who helped develop the Sergeant's collars, "I'd recommend that you use both." The collars mimic a soothing pheromone that mother cats emit while nursing, and Ceva's diffusers and sprays use a synthetic version of a facial pheromone—which cats leave behind when they rub their cheeks on furniture or people—that signals that the territory is safe and secure.

Many veterinarians have embraced synthetic pheromones, recommending them for use at home as well as in cat carriers. The success of these products has cut down on expensive sessions with animal behaviorists.