Intermediate level discussion of poppers that includes physiological experiences, the chemistry behind nitrites, purchase points and product evaluations. Also includes recipes and other popper-related Do It Yourself activities and training videos.
Eye of Mordor
Poppers were first synthesized in 1844 by Antoine Jérôme Balard, but it took the sexual revolution and the disco scene in the 1960s to popularize their use as a recreational drug and fisting facilitator.
When inhaled, the active ingredient in poppers (NO2—) triggers certain physiological responses and some health-related concerns.
There is very little scientific research into how poppers interact with the body. The most die-hard popper enthusiasts have theorized what causes the various physiological responses by extrapolating commonalities from studies on laughing gas (N2O), by basic knowledge of human physiology, and by personal experience.
Poppers and Fisting
At least three primary physiological effects of amyl/butyl nitrites can enhance fisting experiences: smooth muscle relaxation, increased sensitivity, increased libido.
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Measured Physiological Response
Huffing poppers generally causes the following reactions/responses in your body:
03 - 10
Your first inhale results in a feeling of lightheadedness and inner tingle. Your nervous system triggers the relaxation of smooth muscle tissue, specifically within your circulatory system.
11 - 25
Your skin tingle and environmental awareness increase while your head, face, and chest flush with color. Your blood pressure begins to drop precipitously. Your libido increases, and your remaining smooth tissue relaxes (your hole opens up for deeper penetration). During the next 15 seconds, you will have the most success surpassing previous fisting limits.
26 - 35
Your heart begins to pump with tremendous force, and your heart rate begins to accelerate to accommodate the dilated blood vessels.
36 - 60
Your breathing becomes deeper and without training, much more rapid as your body requests air—all systems of your body are reacting fully to the hit. Your senses are at their peak, demanding attention.
61 - 90
Your poppers rush dissipates, and the heart begins to restore normal BP. You notice your heartbeat all over your body. Your cock begins to deflate (if not stroked or inhibited by a cock ring).
91 - 180
Your heart begins to pump normally and its BPM return to normal. Your head begins to ache in response to the heavy flow of blood.
Vasodilation Effects (Short Term)
Vasodilation refers to the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins (called venodilators), large arteries, and smaller arterioles. When blood vessels dilate, the flow of blood is increased due to a decrease in vascular resistance; therefore, dilation of arterial blood vessels (mainly the arterioles) decreases blood pressure.
Short term side effects of popper vasodilation may include: chest pain, heart palpitations and irregularities (fluttering or pounding heartbeat), rapid heartbeat, fluid retention, nausea or vomiting, dizziness, headache, flushing, and nasal congestion.  Individuals with heart conditions should consult a physician before inhaling poppers.
Extreme popper use and certain amyl or butyl isomers can cause blue lips, blue nails, and even blue dick.
The medical term for this condition is cyanosis, after the color CYAN. While cyanosis can normally have many causes, with poppers, it is due to a buildup of methemoglobin inside the bloodstream.
'Poppers catalyze the enzyme that keeps methemoglobin levels in the blood low by turning it into hemoglobin (which is necessary for proper oxygen exchange with our cells). The buildup of methemoglobin in our blood causes the paleness/blueness of skin and lips, etc. There isn't much you can do to avoid this if you're popping [hitting poppers]. It's not necessarily dangerous unless you have certain conditions, in fact if you were to measure your blood oxygen level you'd see that it's normal. However, too much methemoglobin in your blood can be a problem, so like anything just be careful and remember to let your body recover.' 
Nitric oxide regulates the photoreceptor functionality in the eye. When inhaling poppers, the extreme saturation of nitric oxide can result in a temporary disruption of normal eye functions which can lead to long term damage. Case studies have shown complete loss of vision, blurred vision, or blockage of visual fields.
Studies show that an increased consumption of sodium nitrites (in bacon, ham, and other processed meats) has a 67% increase in likelihood of pancreatic cancer. Some theories infer poppers could also increase cancer rates, but there are no studies to confirm these speculations.
Amyl and butyl nitrites are classified as depressants. They bond temporarily with opioid receptors inside the body and once released, can cause fatigue and depression due to chemical imbalances. Users report this haze takes as little as 30 minutes or as much as 6 hours to wear off. Some users aren't adversely affected at all.
Vasodilation, methemoglobinemia, and retinal stimulation can all contribute to headaches, including migraines.
Loss of Erection(s)
Even though they are vasodilators like Viagra and Cialis, with repeated and heavy use, they tend to kill a boner instead of make one harder. This is true especially for men of older age. It is helpful to attain wood first with a tight cock ring before taking hits.
Fisting Tips with Poppers
Keep a handful of Ricola cough drops to use if you get congested. Your sinuses will open up so you can resume powerful hits and deep play.
Hydrate during play and pop several aspirin once the session ends to reduce or eliminate headaches.
Apply artificial tears before and after a hot shower to help your tear ducts recover from the drying effects of nitrites.
The active ingredient in poppers that causes the euphoric rush is the molecule nitrite (NO2). Nitrite refers to two oxygen bonded to a nitrogen molecule, and should not be confused with nitrate, which has a third oxygen molecule (NO3). Although poppers are commonly referred to as amyl nitrate, this is incorrect. Amyl nitrate is (and always has been) a diesel fuel additive.
Attached to the nitrite module is a string of carbon:
A four-carbon string (C4H9-), commonly referred to as butyl, or
A five-carbon string (C5H11-), commonly referred to as amyl (officially as n-pentyl).
Various different prefixes represent how the carbon is organized. The most common are iso, which indicates the molecule has multiple siblings with the same atomic make-up, and cyclo which indicates the carbon atoms are bonded together in a ring.
Poppers were either simple amyl- or isobutyl- nitrites in their original format; however, legal restrictions (EU), production costs, and market forces have introduced various formulas to the popper huffing world. Those formulas include some hexyl isomers, various butyl isomers, and the eight amyl/pentyl isomers.
The preceding section is based on my basic understanding of organic chemistry and my personal study; however, I'm no expert—nor claim that the information is correct. All attempts have been made to limit the information presented to simple facts. Most popper web sites report incorrect data.
Chemical Properties (Maintaining Freshness)
The chemical properties of amyl- and isobutyl- nitrates has played an important role in popper packaging. The carbon/nitrite bond is not strong enough to maintain integrity when subjected to the normal environments of our daily lives (light, temperature, and air). As a result, poppers were originally sold in single-use, breakable glass vials to maintain potency. Since this packaging doesn't accommodate sexual play, manufacturers have designed packaging to address these issues:
Bottles are made of dark glass to reduce light-induced reagents.
Airtight caps prevent the atmosphere from continually reacting with the nitrite.
Labels suggest storing poppers at lower temperatures to keep them fresher longer.
Desiccation capsules or powder in the bottles prevents excessive water build up in your bottle.
Brands and Vendors
There are several manufacturers providing poppers to the market; however, the end product is only available at adult stores and online. These are my primary online sources:
Popperbating helps you goon-up on poppers and release a pent-up load. From a fisting perspective, popperbating videos—often called 'popper trainers'—are helpful for personal stretch sessions with toys. There are two types of popper training videos. The first type (and most common video), is compilation sequences with porn integrated with clips from every-day guys jerking off. The second type involves a trainer conducting a one-on-one popperbate session.
By far, the best source for one-on-one training videos is PoppersGod. He's kink-friendly (though probably not a fister), and you can commission a related popper training video for a small tribute.