The drug alters mood in different ways, depending on how it is taken. Immediately after smoking or intravenous injection, the user experiences an intense "rush" or "flash" that lasts only a few minutes and is described as extremely pleasurable. Smoking or injecting produces effects fastest, within five to ten seconds. Snorting or ingesting orally produces euphoria - a high but not an intense rush. Snorting produces effects within three to five minutes, and ingesting orally produces effects within 15 to 20 minutes.
In all forms, the drug stimulates the central nervous system, with effects lasting anywhere from 4 to 24 hours. Methamphetamine use can not only modify behavior in an acute state, but after taking it for a long time, the drug literally changes the brain in fundamental and long-lasting ways. It kills by causing heart failure (myocardial infarction), brain damage, and stroke and it induces extreme, acute psychiatric and psychological symptoms that may lead to suicide or murder.
Harder to spot is the occasional user who takes meth for parties or raves. This group can hide the effects of meth along with those of alcohol withdrawal and claim a hangover. In fact, using methamphetamine this way is particularly dangerous, because users can drink large amounts of alcohol without passing out. The result is someone who is completely drunk but still awake enough to do damage to themselves or others. Sometimes, this can lead to a fatal alcohol poisoning as an user continues to drink.
Over time, meth addicts gradually lose their ability to feel pleasure in normal activities. Only more of the drug will help the condition, called anhedonia. Users will cycle through periods of ever deepening depression and an unwillingness to participate in their own lives. Job loss and ruined relationships are the common result.
Explosive violence and aggression may also emerge as the addict’s personality begins to change in response to chronic use of the drug. Irritability is common, as well as an inability to deal with the normal setbacks in life. They come to realize they are addicted, and this, combined with the depression that comes with meth addiction, can drive them to seek out more opportunities to use. The vicious cycle continues as the only good feelings the addict ever gets are from meth. Extended binges start to occur and these are followed by long and difficult recovery periods.
Fatal kidney and lung disorders, brain damage, liver damage, blood clots, chronic depression, hallucinations, violent and aggressive behavior, malnutrition, disturbed personality development, deficient immune system, and methamphetamine psychosis (a mental disorder that may be paranoid psychosis or may mimic schizophrenia).
Babies can be born methamphetamine addicted and suffer birth defects, low birth weight, tremors, excessive crying, attention deficit disorder, and behavior disorders. There is also an increased risk of child abuse (including "shaken baby syndrome") and neglect of children born to parents who use methamphetamine.
A toxic reaction (or overdose) can occur at relatively low levels, 50 milligrams of pure drug for a non-tolerant user. Metabolic rates vary from person to person, and the strength of the illegal form of the drug varies from batch to batch, so there is no way of stating a "safe" level of use. In overdose, high fever, convulsions and cardiovascular collapse may precede death. Because stimulants affect the body's cardiovascular and temperature-regulating systems, physical exertion increases the hazards of meth use.