Users will feel the effects usually within 30 seconds of injecting it.

Shooting meth produces a quicker and more intense high than ingesting it any other way. Injecting meth, shooting up, or “slamming” is the most dangerous way to ingest the substance. “Meth” can be ingested by either oral consumption, snorting, smoking, or injecting it. Medically, it is sometimes indicated for the treatment of ADHD and as a short-term weight-loss aid, but it is more widely used as an illicit substance. Methamphetamine is a Schedule II stimulant that is rarely prescribed legally. These characteristics make it a drug with high potential for widespread misuse. It also has longer-lasting and more harmful effects on the central nervous system. However, methamphetamine differs from amphetamine in that, at comparable doses, much greater amounts of the drug get into the brain, making it a more potent stimulant. Like amphetamine, methamphetamine causes increased activity and talkativeness, decreased appetite, and a pleasurable sense of well-being or euphoria. The National Institute on Drug Abuse discusses methamphetamine and what it does:

Methamphetamine was developed from its parent drug amphetamine and was originally used in inhalers and nasal decongestants. Meth is also called ice, blue, or crystal. It is a white, odorless, and bitter-tasting powder that dissolves easily in water or alcohol. Methamphetamine or “Meth” for short is a very addictive and powerful stimulant that affects the central nervous system and produces an intense and powerful euphoria in its users.

Where to inject meth