Poppers are the broad name for chemicals called alkyl nitrites sold under a wide variety of brand names. Since they're illegal for use as a drug, but have some use as a solvent, you'll see them identified as "video head cleaners" (remember video tape machines?), "leather cleaners," and other random uses. But it's their affect on you when you inhale the fumes that drives interest in them.
You'll see chemical names like amyl nitrite, butyl nitrite, isobutyl nitrite. Some people claim that certain versions have better or worse effects on them (personally, my best experiences have been Jungle Juice Platinum which is amyl nitrite). But chemically, it's the nitrite part of the chemical combo that has its effect on your body.
Physically it's a vaso-dilator: it causes your blood vessels to open up wider and move more blood. That dilation has an effect of also causing smooth muscle to relax, which is why it's popular with people who want to be penetrated anally and want their sphincter to relax to make entry more pleasurable.
The sensation you feel during this will be a rush of blood in the head, few moments of euphoria, some dizziness, maybe a sense of falling or the room spinning. It's actually quite similar to the sensation of standing up too quickly or a really good stretch when you're tired; you'll feel the blood rushing and get a little dizzy. For some people this can intensify the pleasure of sex, especially the moment of orgasm. For others it may help in prolonging the time to orgasm by making it harder to focus.
But because of the change in blood flow, it can also give you a splitting headache that can last for up to an hour. The intensity of the effect, and any headaches, can range with how much you do, how deeply or how many times you inhale. So it's essential to go slowly until you know what's right for you. For some people, it goes right to headache without much fun. For others, once you find the right brand and chemical make-up that works for you, it can be fun once you've dialed in exactly how much works for you and what precise feelings and sensations it evokes. People get different things from it and only you will know if these are positives, negatives, or neutral for you.
Now the downsides: Because it screws with your blood vessels and blood flow, if you have a heart condition it can exacerbate your issues. Although inhaled nitrites were used originally to help people with chest pain from clogged coronary arteries (replaced by nitroglycerine tablets), if you've got a heart condition it's definitely not something to fuck around with unless your doctor says its ok. (And yes, in many cities you can find "sex positive" doctors who will openly talk to you about sexual practices and while they may not recommend using poppers, they can tell you they would be overly dangerous for you.) So you're definitely advised to ask your doctor if you think you might have any heart concerns. And if you don't have a doctor you can talk with openly about this, it might be time to get acquainted with a new doctor, perhaps one at a reproductive health clinic like Planned Parenthood or an STI screening clinic who might be more open to talking with you about your situation.
Other downsides: The liquid is highly flammable, so keep it away from open flames. It's also very bad for your skin, especially mucus membranes, so sniffing it right out of the bottle can be a dicey prospect (and is why some people use things that look like a metal lipstick case with a cotton ball soaked in the fluid to inhale from rather than the whole bottle). It's also very staining, so don't spill it. And because it's a volatile compound, it goes "bad" quickly. You can keep it in the freezer or refrigerator to help prolong the life, but don't expect it to last more than a few months once it's been opened, and since good stuff is expensive, you can find your investment worthless faster than you might have hoped.
Here are some good information sources that might help you learn more:
www.urban75.com: Drugs - Amyl, Butyl or Isobutyl Nitrite, Nitrates, Poppers
www.eypdas.org.uk: The Facts About Poppers | The Effects Of Poppers
www.project6.org.uk: Poppers | Information & Advice
Poppers Guide
As for where to get them, many states have cracked down on the sale of poppers. You can still find them online, you just may have to be creative in your search terms. Many sex shops will sell them as well. The brand names are all pretty well known and often only differ in the specific chemical compound they contain: Rush (isobutyl), Jungle Juice and Jungle Juice Platinum (amyl), Jacked (isobutyl). You can even find some of these sold on Amazon, though many are independent sellers using the Amazon platform and could be of sketchy quality. It's best to find places that you feel are reputable (recommended by friends, been around a long time, seem serious about their quality, have good online reputations, etc.) because especially with the well-known brands like Jungle Juice, they attract counterfeiters and god only knows what they actually have in them. Personally, I buy mine from a good quality sex shop here in my city. But you can find some reputable places in other cites and even a few still operating online.
Good luck!
