The Athletics Integrity Unit (AIU) dropped a bombshell on Thursday, provisionally suspending women’s marathon world record holder, Ruth Chepng’etich, after she tested positive for Hydrochlorothiazide (HCTZ), a banned diuretic.
The AIU revealed that Chepng’etich’s positive sample was collected on March 14, just five days after her only race of the 2025 season. So, what exactly is HCTZ?
Hydrochlorothiazide is a thiazide diuretic, commonly known as a “water pill”, prescribed clinically to manage hypertension and fluid retention. However, in sports, its misuse is a red flag.
HCTZ appears under Class S5 (Diuretics and Masking Agents) on the World Anti-Doping Agency (WADA) Prohibited List. Substances on this list are grouped into categories.
S0 non-approved substances, S1 anabolic agents, S2 peptide hormones, growth factors, related substances and mimetics, S3 beta-2 agonists, S4 hormone and metabolic modulators, S5 diuretics and masking agents. Diuretics like HCTZ are banned for two critical reasons:
First, by reducing water retention, they lower an athlete’s body weight, a key performance factor in endurance and speed disciplines. Secondly, they dilute urine, reducing the detectable concentration of prohibited substances or their metabolites, making it harder for anti-doping labs to catch cheats.
Masking agents, on the other hand, work by making drug tests ineffective, leading to false-negative results.
The AIU said HCTZ is used clinically to treat fluid retention and hypertension, adding that diuretics may be abused to mask the presence in urine of other prohibited substances. Chepng’etich was formally charged on April 3 but was not immediately banned.
Instead, she opted for a voluntary provisional suspension on April 19 as the AIU began its investigations.
"A Notice of Charge has been issued against Chepng'etich regarding the detection of the prohibited substance."
"Chepng'etich was not provisionally suspended by the AIU at the time of notification; however, on 19 April, she opted for a voluntary provisional suspension while the AIU’s investigation was ongoing."
Chepng’etich shot to global stardom after her astonishing 2:09:56 victory at the 2024 Chicago Marathon, obliterating the previous world record of 2:11:53 set by Ethiopia’s Tigst Assefa at the 2023 Berlin Marathon.
She became the first woman in history to break both the 2:11 and 2:10 barriers, a feat once deemed impossible in women’s marathon running.
