Highly flammable liquid, can catch fire and cause burns from cigarettes, cigars, candles, lighters etc.
Poisonous and potentially fatal if swallowed
Chemical burns if splashed on skin.
Temporary difficulty in maintaining erection
Drops blood pressure, possibly to dangerous levels if you have low blood pressure already
Nitrites reduce immune functioning when used regularly overtime
Can make it hard to get sexual aroused without poppers, if regularly paired with sexual activity over a period of time.
Can contribute to compulsive masturbation, as poppers can increase pleasure and intensity of masturbation.
Amyl and Butyl/Isobutyl Nitrites are harder to find: they are illegal, as they can be cancer-causing with long-term, regular use.
Isopropyl Nitrite can damage eye cells. Short-term, blurry vision can clear up by ceasing poppers use. Longer-term vision problems can result from prolonged, long-term use. Check out a related study here.
Dangerous Drug Combinations
Erectile Drugs, when taken with Poppers, can cause a fatal drop in blood pressure
Heart/Blood Pressure Medications mixed with Poppers can cause a fatal drop in blood pressure