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Triparanol
Clinical data
Trade names	MER/29
Other names	Metasqualene
ATC code	None;
Identifiers
	IUPAC name 2-(4-Chlorophenyl)-1-[4-[2-(diethylamino)ethoxy]phenyl]-1-(4-methylphenyl)ethanol;
CAS Number	78-41-1;
PubChem CID	6536;
ChemSpider	6288;
UNII	63S8C3RXGS;
ChEBI	CHEBI:135714;
CompTox Dashboard (EPA)	DTXSID6046507 ;
ECHA InfoCard	100.001.014
Chemical and physical data
Formula	C27H32ClNO2
Molar mass	438.01 g·mol−1
3D model (JSmol)	Interactive image;
	SMILES CCN(CC)CCOc1ccc(C(O)(Cc2ccc(Cl)cc2)c2ccc(C)cc2)cc1;
	InChI InChI=1S/C27H32ClNO2/c1-4-29(5-2)18-19-31-26-16-12-24(13-17-26)27(30,23-10-6-21(3)7-11-23)20-22-8-14-25(28)15-9-22/h6-17,30H,4-5,18-20H2,1-3H3; Key:SYHDSBBKRLVLFF-UHFFFAOYSA-N;

Triparanol (INNTooltip International Nonproprietary Name, BANTooltip British Approved Name; brand name and development code MER/29, as well as many other brand names) was the first synthetic cholesterol-lowering drug.^[1]^[2] It was patented in 1959 and introduced in the United States in 1960.^[3]^[4] The developmental code name of triparanol, MER/29, became so well known that it became the registered trade name of the drug.^[5] It was withdrawn in 1962 due to severe adverse effects such as nausea and vomiting, vision loss due to irreversible cataracts, alopecia, skin disorders (e.g., dryness, itching, peeling, and "fish-scale" texture), and accelerated atherosclerosis.^[3]^[2] It is now considered to be obsolete.^[3]^[2]

The drug acts by inhibiting 24-dehydrocholesterol reductase, which catalyzes the final step of cholesterol biosynthesis, the conversion of desmosterol into cholesterol.^[6] Although effective in reducing cholesterol levels, this results in tissue accumulation of desmosterol, which in turn is responsible for the side effects of triparanol.^[2] Unlike statins, triparanol does not inhibit HMG-CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis,^[2] and in contrast to triparanol, statins can lower cholesterol levels without resulting in accumulation of intermediates like desmosterol.^[2]

Estrogen is known to lower cholesterol levels, but produces side effects like gynecomastia and decreased libido in men.^[3] It was hoped that a drug could be developed that lacked overt estrogenic effects but still lowered cholesterol levels.^[3] Triparanol is a triphenylethanol and was derived from chlorotrianisene (TACE), a nonsteroidal triphenylethylene estrogen.^[3]^[7] The nonsteroidal triphenylethanol antiestrogen ethamoxytriphetol (MER-25) is a derivative of triparanol.^[8] The selective estrogen receptor modulator clomifene is also structurally related to triparanol.^[7]^[9] The developers of triparanol jokingly referred to it as a "non-estrogenic estrogen" due to its lipid-lowering effects without other estrogenic effects.^[3]