• The drug is inhaled through the nose or mouth.
• It may be sprayed into a plastic bag, poured into a bottle or soaked into a cloth or sleeve before being inhaled.
• Some drugs are inhaled directly from the container.
• Sometimes they are sprayed directly into the mouth or nose.  This can be very dangerous and cause suffocation
• The effects of inhalants may start to be felt immediately and can last for 45 minutes.

The symptoms of overdose include:

• hallucinations
• drowsiness and coma.

Some inhalant-related deaths are thought to have been caused by a condition called ‘sudden sniffing syndrome’. This is a type of heart failure that can strike if the user attempts any physical exertion after inhaling.

Users have also been accidentally killed by engaging in risky behaviours, such as jumping off high buildings while under the influence.

• feeling disoriented
• decreased coordination
• visual distortions
• nausea, vomiting and diarrhoea
• headaches
• bloodshot eyes
• increased confidence leading to risky behaviour
• hallucinations
• blackout, convulsions, coma

Sudden sniffing death

• lowered inhibitions
• feeling of wellbeing
• excited, euphoric, giggling and laughing
• stimulation
• initial rush or high
• get “off my head”
• nitrites enhance sexual experience
• decrease social anxiety
• common peer group activity

Glue, gas, sniff, huff, chroming, poppers

• malnutrition and rapid weight loss due to reduced appetite
• chronic sleeping problems
• reduced immunity and increased susceptibility to infections due to not sleeping or eating properly
• cracked teeth and other dental issues from jaw clenching, teeth grinding, dry mouth and poor hygiene
• high blood pressure and rapid and irregular heartbeat, placing stress on the heart and increasing the risk of heart-related complications such as heart attack and heart failure
• increased strain on the kidneys which may result in kidney failure

• increased heart rate, breathing and body temperature
• decreased appetite
• jaw clenching; teeth grinding
• nausea and vomiting;
• dry mouth
• changes in libido
• nervousness, anxiety, agitation, panic, paranoia
• hallucinations
• repetition of simple acts
• irritability, hostility, aggression
• feelings of increased strength
• itching, picking and scratching
• headaches; dizziness
• difficulty sleeping
• abrupt shifts in thinking and speech
• dilated pupils (enlarged)

• People who use methamphetamines on a regular basis may become dependent on them
• They may also develop a tolerance to methamphetamines, which means they will need to use larger amounts to get the same effect.
• People who become dependent on methamphetamine typically inject or smoke the drug and use it at least twice per week.
• Dependence on methamphetamines can be psychological, physical or both. People who are dependent crave methamphetamine and find it very difficult to stop using it.

In the brain, a primary action of methamphetamine is to elevate the levels of extracellular monoamine neurotransmitters (dopamine, serotonin, norepinephrine) by promoting their release from the nerve endings.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2413312/