When Viagra hit the market in 1998, if you were old enough to pay attention, the idea of needing what the internet now loves to call boner pills probably seemed remote. However, erectile dysfunction (ED) is pretty common: Mild and moderate ED affects about 10 percent of men per decade of life—that’s roughly 40 percent of guys in their 40s, 50 percent in their 50s, and so on. And as men age, they require more stimulation, more time between erections, and in many cases, a little help from the pharmacy.

Sildenafil, the active ingredient in Viagra, was originally developed in the early 1990s to treat cardiovascular disease. It was meant to dilate the heart’s blood vessels by blocking a protein called phosphodiesterase type 5, or PDE-5. In human clinical trials, however, sildenafil caused an unexpected side effect: the dilating blood vessels were in the penis, not the heart. And so the “potency pill” was born.

In the years since, three other PDE-5 inhibitors have come to market: Cialis, Levitra, and Stendra. Though researchers continue to investigate new therapies and alternative treatments, PDE-5 pills are still the go-to treatment for most guys who need a little help getting it up.

They’re all generally the same, but they’re also different. All of four of the PDE-5-inhibiting drugs approved for use in America stimulate erections through the same chemical reaction. Yet, says Adam Murphy, MD, a professor of urology at Northwestern University’s Feinberg School of Medicine, “guys respond to different pills in different ways.”

Choosing between one and another is often a matter of trial and error. Here’s how you can know which boner pill, as they say, is right for you.

Viagra

Still the leading brand in ED pills, Viagra should be taken at least an hour before sex and on an empty stomach. That makes it difficult to have a romantic dinner before adjourning to the bedroom. It’s also known to cause side effects that include blurry vision, altered color perception, rashes, flushing, and headaches. But Viagra reliably provides a strong erection, usually the first time it’s used, and can produce multiple erections for up to four hours. More than a dozen clinical studies have shown good results for men with diabetes as well as guys who’ve had prostate surgery or spinal cord injuries.

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Cialis

Rather than Viagra’s 50 or 100 mg blue pills, Cialis comes in lower doses, the smallest of which is just 2.5 mg. That allows for daily use, ensuring the drug’s always in your system when you’re ready for sex. Dr. Murphy says Cialis can be taken whenever you want and allows for more spontaneous sexual activity. The pills are available in strengths as high as 20 mg, and hangs around your bloodstream for up to 36 hours. Popping Cialis has some side effects—it increases your chances of limb, back and muscle pain. But if your erectile dysfunction is connected to an enlarged prostate, the med’s a great choice, since the drug’s approved to treat both conditions.

Levitra

Perhaps Viagra’s closest cousin, Levitra takes a solid hour to kick in and lasts up to 4 hours. It’s about as effective as sildenafil when it comes to raising your sail, though studies have shown Levitra is more potent and more selective than sildenafil at inhibiting PDE-5, meaning the drug does a better job of moving blood to the penis rather than other parts of the body. Levitra also wins out over Viagra when it comes to side effects: it doesn’t cause vision problems or limb pain. It comes in doses ranging from 5 mg up to 20, as well as more easy-to-hide tablets that disintegrate under the tongue.

Stendra

The newest of the PDE-5 inhibitors, Stendra was engineered “to limit non-penile side effects,” says Dr. Murphy. Sore throats are common, but not dizziness, vision changes, nausea, or muscle aches. It’s also the fastest of the bunch: taken in 100-mg and 200-mg doses, it can produce an erection in as little as 15 minutes. And eating doesn’t reduce its effectiveness.

How to get more bang for your buck
Generic versions of Viagra (sildenafil), Cialis (tadalafil), and Levitra (vardenafil) have all become available in the last few years. They’re the same drugs, just without the fancy packaging and expensive TV commercials. That’s great news because it’s brought the cost of the meds way down, and has made ED treatments more available to a greater number of men. Full retail price for Viagra can run as much as $85 for a single 100 mg tablet. The generics cost much less, and—in the case of sildenafil—come in 20 mg doses. “Instead of taking one pricey 50 or 100 mg Viagra, a man can take two, four, or even five generic sildenafils, which cost only a few cents each,” says New York-based urologist Elizabeth Kavaler, M.D., a Men’s Health advisor.

Don’t skip the good stuff

Dr. Kavaler is glad that more ED pills are available at lower prices, but she also worries that the pills can tempt guys into thinking of sex is only about intercourse. If you’re aiming for a steamy evening, it’s important to remember the power of foreplay, as well as good lubes and ointments.

“An erection is a response of the parasympathetic nervous system,” Dr. Kavaler says. “The more sensitized your nervous system is to the act of sexual function, the more your body will respond.” She likens intercourse to dessert at the end of a good meal: the more you can prolong the experience, the more you’ll enjoy it. Sometimes having the pills at the ready, in your overnight bag or medicine cabinet, can give you that little extra boost of confidence when it comes to having great and satisfying sex.