The 27-year-old Troicki was found guilty of failing to provide a blood sample during a drugs test at the Monte Carlo Masters in April.
"Mr Troicki provided a urine sample, but did not provide a blood sample," said an ITF statement.
"He asserted to an independent tribunal that he was assured by the doping control officer (DCO) that it would be acceptable not to provide a sample on account of him feeling unwell that day.
"However, the tribunal concluded that the DCO told Mr Troicki that she could not advise him as to whether his reason for not providing a blood sample was valid, and that no such assurances were given by her."
His failure to provide a blood sample at Monte Carlo, where he was knocked out in the first round, constituted a dope test failure, said the ITF, despite the player's insistence that he was under stress at the time.
"The tribunal determined that he is suspended from participation for a period of 18 months, and so ending at midnight on 24 January 2015," added the statement.
Troicki, who is currently at 53 in the world, reached a career high 12 in 2011 and has won $4.5 million (3.4 million euros) in prize money.
His only tour title came in 2010 when he captured the Moscow indoors event.
That same year, he won the decisive fifth and final rubber against France as Serbia claimed the Davis Cup for the first time.
Troicki was playing at the Umag claycourt event in Croatia on Thursday where he was beaten 6-0, 6-4 in the second round by Spanish veteran Tommy Robredo.
His best results in 2013 have all come on clay with quarter-final runs in Bucharest, Munich and Dusseldorf.
Troicki is the third tennis player caught up in doping violations in 2013.
In May, Brazil's Fernando Romboli, the world number 693, was handed an eight and a half month ban for testing positive for the banned diuretics, furosemide and hydrochlorothiazide.
Czech player Barbora Zahlavova Strycova was banned for six months in February after testing positive for sibutramine, a substance found in a weight-loss product.
The former world number 39, now at 120, failed a drugs test at the Luxembourg Open in October last year.
In March this year, the ITF announced that the sport would follow the example set by cycling and introduce biological passports.