Methamphetamine is a stimulant drug. A form of the drug known as methamphetamine hydrochloride, marketed as Desoxyn, is a Food and Drug Administration (FDA)-controlled substance used to treat attention deficit hyperactivity disorder (ADHD) and obesity.

Adderall (amphetamine) and Ritalin (methylphenidate) are related FDA-approved drugs that have typically been used to treat ADHD in adolescents.

Other, illegal forms of methamphetamine—usually in the form of a white powder—can be recreationally snorted or dissolved in water and injected.

Crystal meth is a solid, crystalline form of the drug. It may look like shards of glass or clear-white rocks.

Users often smoke or snort crystal meth. Smoking the drug can quickly elevate levels of methamphetamine in the brain. This gives users a rapid, intense high, making crystal meth both more addictive and potentially more harmful than other forms of methamphetamine.

American pharmaceutical company Smith, Kline, and French began marketing the amphetamine inhaler for use in asthma and nasal congestion in 1932.

Their inhaler medication, called Benzedrine, was initially available without a prescription. People soon discovered its euphoric, energizing side effects.

Because of these stimulant-type effects, pharmaceutical companies began to manufacture Benzedrine in pill form for narcolepsy (a sleep disorder).

During World War II, German pharmaceutical company Temmler marketed methamphetamine tablets as a nonprescription drug under the brand name Pervitin.

Methamphetamine triggers a response in the body that’s similar to adrenaline, heightening alertness and a willingness to take risks.

Japanese, U.S., British and German military personnel are reported to have used the stimulant to enhance endurance and ward off fatigue on long campaigns.

Kamikaze pilots received high doses of Pervitin before suicide flight missions. Japanese factory workers also used methamphetamine to work longer hours.

The German army ordered front-line soldiers and fighter pilots to take military-issued stimulants that contained a combination of methamphetamine and cocaine.

Recreational use of Benzedrine—or bennies—became a popular part of Beatnik culture in the 1950s. Many so-called “Beat Generation” writers, including author Jack Kerouac and poet W.H. Auden, reportedly used artificial stimulants, including bennies.

But amphetamine use began falling out of favor in the late 1950s. In 1959, the FDA began to require prescriptions for Benzedrine.

It was also becoming apparent that amphetamines had many harmful effects—including delusions, paranoia, abnormal heartbeat and heart failure—among regular users and addicts.

Chronic methamphetamine use can lead to addiction. Over time, the brain develops tolerance to the drug and the user needs to take higher and higher doses to achieve the same pleasurable effects.

Crystal meth may be particularly addictive. Some users report getting hooked after trying the drug just once.

Meth addiction can cause serious changes in the brain including paranoia, hallucinations and delusions (for instance, the feeling of insects creeping under the skin).

Many meth addicts have rotting teeth—a condition known as meth mouth—and experience severe weight loss.

In the 1980s, the United States began to tighten regulations around the sale and use of the ephedrine–a pharmaceutical precursor used to make crystal meth. As a result, illegal meth labs turned to an easier to obtain precursor—pseudoephedrine—a chemical found in many cold medicines.

Use of crystal meth in the United States exploded in the early 1990s. Between 1994 and 2004, methamphetamine use rose from just under two percent of the U.S. adult population to approximately five percent.

In 2006, the United Nations World Drug Report called meth the most abused hard drug on Earth.

Meth use has declined over the past decade, possibly as a result of limits put on the sale of pseudoephedrine in many countries. In the United States, in 2012, roughly 1.2 million people (about 0.4 percent of the U.S. population) reported using meth in the past year.

While Adderall and Ritalin have some chemical properties in common with methamphetamine, they are generally considered safer when taken at prescribed doses and under the supervision of a medical practitioner. Misuse of the drugs, however, can lead to addiction.

Use of prescription stimulants, notably Adderall, in the U.S. adult population has climbed in recent years. In 2012, adults between the ages of 20 and 39 received roughly 16 million Adderall prescriptions.

A New York Times story published in 2016 referred to millennials as “Generation Adderall,” for liberal use of the drug in young adults, with or without a prescription.