The most-used illegal substances

Methamphetamine, known by a variety of street names, including meth, crystal, glass, and ice, is an extremely addictive stimulant that is usually found as a white, odorless, bitter-tasting crystalline powder.

It is currently the most-used illegal recreational drug in China.

Methamphetamine increases the amount of the neurotransmitter dopamine, leading to high levels of the chemical in the brain. Dopamine is involved in reward, motivation, the experience of pleasure, and motor functions. Its ability to release dopamine rapidly in the "reward regions" of the brain produces a euphoric "rush" or "flash" that many users experience.

Recreationally, methamphetamine's ability to raise energy levels has been reported to lift moods and increase sexual desire.

Ketamine, also known as "Vitamin K" if ingested or "Ketaject" if injected, is a dissociative drug that contains hallucinogens that make the user feel detached from reality.

The second-most popular illegal synthetic drug in China, ketamine can cause dream-like states and hallucinations.

Users report sensations ranging from a pleasant feeling of floating to being separated from their bodies. At high doses, users reported "out of body" or "near-death" experiences.

Low-dose intoxication from ketamine can impair attention, learning ability and memory. In high doses, ketamine can cause delirium, amnesia, impaired motor function, high blood pressure, depression and potentially fatal respiratory problems.

Because of the detached, dreamlike state it induces, where the user finds it difficult to move, ketamine has been used as a "date-rape" drug. It is commonly used in the medical field as an animal tranquilizer.

Organic drugs

Heroin is an opiate synthesized from morphine, a naturally occurring substance extracted from the seed pod of the Asian opium poppy plant. The drug usually appears as a white or brown powder, or as a black sticky substance known as Black tar heroin.

If injected, users report a surge of euphoria ("the rush") accompanied by a dry mouth, a warm flushing of the skin, heaviness of the extremities and clouded mental function. Following the initial euphoria, the user goes "on the nod", an alternately wakeful and drowsy state. Users who do not inject the drug may not experience the initial rush, but the other effects are the same.

Cocaine, a powerfully addictive stimulant made from the leaves of the coca plant, native to South America. It produces short-term euphoria, energy and talkativeness, in addition to potentially dangerous physical effects such as increased heart rate and raised blood pressure.

The drug creates a strong feeling of exhilaration. Users often feel invincible, carefree, alert, euphoric and energetic. This feeling is usually followed by agitation, depression, anxiety, paranoia and decreased appetite.

Marijuana is made from the dried leaves, flowers, stems and seeds of the hemp plant. It includes an active ingredient called THC that produces an intensely laid-back feeling.

Users usually smoke the drug via hand-rolled cigarettes or pipes. It can be also mixed in with food, such as brownies, cookies or candies, or brewed as a tea.

The immediate effects include relaxation and mild euphoria, a general alteration of conscious perception, increased awareness of sensation, increased libido and distortions in the perception of time and space.

At higher doses, effects can include altered body image, auditory or visual illusions, pseudo-hallucinations and ataxia, a loss of muscle coordination.

Sources: The National Institute on Drug Abuse of the United States; The National Institutes of Health; The US Department of Health and Human Services.