Fenethylline is a theophylline derivative of amphetamine having stimulant effects similar to those of other amphetamine-type derivatives. Fenethylline was used as medicament for hyperactivity disorders in children, narcolepsy and depression, but it has also been used as a drug of abuse under the common name of 'captagon'. Unlike other drugs of abuse, the clandestine synthesis of fenethylline is simple, using inexpensive laboratory instrumentation and raw materials legal to obtain. A review of all the existing knowledge of fenethylline is reported, concerning its chemistry, synthesis, pharmacology and toxicology, legislation, its prevalence and use as drug of abuse, as well as its analysis in biological or seized samples. Published or reported captagon-related cases and seizures are also presented. All the reviewed information was gathered through a detailed search of PubMed and the Internet. The primary drug market for fenethylline (as captagon) has traditionally been countries located on the Arabian Peninsula but also North Africa since 2013. In Arab countries, millions of captagon tablets are seized every year which represents one-third of global amphetamines seizures within a year. Furthermore, three of four patients treated for drug problems in Saudi Arabia are addicted to amphetamines, almost exclusively in the form of captagon. Significant information on fenethylline is provided for pharmacologists, toxicologists and forensic pathologists. Fenethylline, although old, has recently been introduced to the drug market, especially in Arab countries. Continuous community alertness is needed to tackle this current growing phenomenon.