Over the years, in particular during the 1980's, suggested connections have been made between the use of poppers and a number of human medical conditions, including AIDS and glaucoma. None of these connections has survived serious scientific scrutiny and to this day there is general agreement amongst objective researchers that there is no hard evidence to suggest that the habitual use of alkyl nitrites for recreational purposes has any detrimental effect on the users health. This is really quite surprising, hard to believe for many, and this makes poppers theoretically the safest - or least harmful - of all recreational drugs currently used in the western world.

The most famous of these suggested connections took place in the 1980's, when medical  researchers noticed a correlation between the use of poppers and the incidence of the HIV virus which causes AIDS. This connection was later decided to be the result of the fact that there is a significantly higher use of poppers in the gay community, a demographic group which also has a significantly higher proportion of AIDS sufferers. This noticed correlation sparked a surge of interest in the connection and considerable research, as many eager researchers battled to be the first to prove the correlation. Unfortunately for the researchers and fortunately for poppers users, the subsequent research proved conclusively that there is no reason to suspect any connection between the use of poppers and AIDS.

Furthermore, according to the 1979 report Isobutyl Nitrite and Related Compounds (know as the Pharmex Report, because it was sponsored by Pharmex Ltd.), authored by Mark Nickerson, John O. Parker, Thomas P. Lowry, and Edward W. Swenson, there is no evidence of dependency, which makes poppers a non-addictive, safe recreational drug.

This said, poppers are nevertheless a drug and alkyl nitrite is a toxic and highly volatile, flammable compound. Users should therefore use poppers recreationally in a responsible and educated manner. Also, it should be pointed out that scientific evidence is not always correct. Scientific researchers who have made extensive studies of the effects of poppers use have not said unqualifiedly that the use of poppers is completely safe. Anyone who states categorically that poppers are safe is overstating the case. What researchers and scientists have said is that there is no demonstrable evidence that alkyl nitrites are unsafe or addictive.
Below is the list of short term negative effects of using poppers and the respective treatment, as outlined in the 1979 Pharmex Report, and their given summary:
 

EFFECT	TREATMENT
Fall in blood pressure (hypotension) and accelerated heart rate (tachycarpia).	Remove from concentrated exposure and and symptons will disappear within 90 seconds without treatment.
Weakness, dizziness and syncope (fainting).	Remove from concentrated exposure, place subject in horizontal position, and symptons will promptly disappear.
Throbbing headache.	Remove from exposure and treat with mild analgesics such as aspirin in rare case not responsive to removal.
Methemoglobinemia.	Potential level is clinically insignificant - and no treatment is required.

Pharmex Report Summary:

All the volatile nitrites can produce vascular dilation with consequent hypotension and headache and insignificant degrees of methemoglobinemia. All effects are transient and can be reversed by removing subject from the area of high nitrite concentration. There is no significant toxicity to the lungs, liver or kidneys. There are minimal irritant properties to the skin and mucous membranes, though contact is painful to the nasal mucosa. No pathological changes have been reported.

Alternative View Points

Not everyone, however, agrees with this scientific analysis, the most notable of whom is John Lauritsen who published, amongst other things, the following short report in 1996 warning about the dangers of poppers:
 

TOXICITIES OF POPPERS (NITRITE INHALANTS)

It is a matter of grave concern that there has been, in the past few years, a resurgence of drug use among gay men. The fashionable gay drugs now seem to be crystal meth, ecstasy, and Special K, as well as such standbys as alcohol, poppers, cocaine, and quaaludes.

Since 1983 I have been trying to warn gay men about the dangers of poppers (volatile nitrites), in collaboration with Hank Wilson of San Francisco, who in 1981 founded the Committee to Monitor Poppers. Our efforts were largely successful. Laws banning poppers were passed by local and state governments, and finally by the U.S. Congress. Many gay men stopped using poppers, as they became aware of their immunosuppressive and carcinogenic properties.

Nevertheless, poppers are being sold again openly in some cities. The miasma of popper fumes has again become a taken-for- granted aspect of the "gay lifestyle".

Poppers are hazardous to the health in many different ways: They damage the immune system. They reduce the ability of blood to carry oxygen. They cause anemia (both Heinz body hemolytic anemia and methemoglobinemia). They damage the lungs. Poppers are powerfully mutagenic (that is, they cause cellular mutations), and they have the potential to cause cancer by producing deadly N-nitroso compounds. Poppers can cause serious skin burns and death or brain damage from cardiovascular collapse or stroke. Poppers have been used successfully to commit suicide (by drinking) and murder. (The victim was gagged with a sock soaked with poppers.)

There are strong epidemiological links between the use of poppers and the development of AIDS, especially Kaposi's sarcoma (KS). In AIDS cases, KS is found almost entirely among gay men who used poppers, not among members of other "risk groups".