Commonly referred to as Ecstasy or XTC, MDMA was first synthesized in 1912 by a German company possibly to be used as an appetite suppressant. Chemically, it is an analogue of MDA, a drug that was popular in the 1960s. In the late 1970s, MDMA was used to facilitate psychotherapy by a small group of therapists in the United States. MDMA was first developed in 1912 by Merck. It was used to enhance psychotherapy beginning in the 1970s and became popular as a street drug in the 1980s. MDMA is commonly associated with dance parties, raves, and electronic dance music. It may be mixed with other substances such as ephedrine, amphetamine, and methamphetamine. In 2016, about 21 million people between the ages of 15 and 64 used ecstasy (0.3% of the world population). This was broadly similar to the percentage of people who use cocaine or amphetamines, but lower than for cannabis or opioids. In the United States, as of 2017, about 7% of people have used MDMA at some point in their lives and 0.9% have used it in the last year. MDMA is often considered the drug of choice within the rave culture and is also used at clubs, festivals, and house parties. In the rave environment, the sensory effects of music and lighting are often highly synergistic with the drug. The psychedelic amphetamine quality of MDMA offers multiple appealing aspects to users in the rave setting. Some users enjoy the feeling of mass communion from the inhibition-reducing effects of the drug, while others use it as party fuel because of the drug's stimulatory effects. MDMA is used less often than other stimulants, typically less than once per week. MDMA is sometimes taken in conjunction with other psychoactive drugs such as LSD, psilocybin mushrooms, 2C-B, and ketamine. The combination with LSD is called "candy-flipping".