Carnitine acetyltransferase belongs to a family of ubiquitous enzymes that play pivotal roles in cellular energy metabolism. Meldonium is a relatively weak inhibitor to carnitine acetyltransferase (when compared to γ-butyrobetaine hydroxylase), with an inhibition constant (KI) of 1.6 mM. Chemistry The chemical name of meldonium is 3-(2,2,2-trimethylhydraziniumyl) propionate. It is a structural analogue of γ-butyrobetaine, with an amino group replacing the C-4 methylene of γ-butyrobetaine. γ-Butyrobetaine is a precursor in the biosynthesis of carnitine. Meldonium is a white crystalline powder, with a melting point of . Society and culture Doping Meldonium was added to the World Anti-Doping Agency (WADA) list of banned substances effective 1 January 2016 because of evidence of its use by athletes with the intention of enhancing performance. It was on the 2015 WADA's list of drugs to be monitored. A high prevalence of meldonium use by athletes in sport was demonstrated by the laboratory findings at the Baku 2015 European Games. 13 medallists or competition winners were taking meldonium at the time of the Baku Games. Meldonium use was detected in athletes competing in 15 of the 21 sports during the Games. Most of the athletes taking meldonium withheld the information of their use from anti-doping authorities by not declaring it on their doping control forms as they should have. Only 23 of the 662 (3.5%) athletes tested declared the personal use of meldonium. However, 66 of the total 762 (8.7%) of athlete urine samples analysed during the Games and during pre-competition tested positive for meldonium. WADA classes the drug as a metabolic modulator, just as it does insulin. Metabolic modulators are classified as S4 substances according to the WADA banned substances list. These substances have the ability to modify how some hormones accelerate or slow down different enzymatic reactions in the body. In this way, these modulators can block the body's conversion of testosterone into oestrogen, which is necessary for females. On 13 April 2016 it was reported that WADA had issued updated guidelines allowing less than 1 microgram per milliliter of meldonium for tests done before 1 March 2016. The agency cited that "preliminary tests showed that it could take weeks or months for the drug to leave the body". Affected athletes On 7 March 2016, former world number one tennis player Maria Sharapova announced that she had failed a drug test in Australia due to the detection of meldonium. She said that she