However, the group paid for his flights with Aer Lingus to New York last July, at a cost of at least €690. Following the treatment, he stayed with a friend in Manhattan for nine days while recovering.
An investigation of the group's finances in the last five years reveals that it has been unable to spend a large amount of the vast sums it raises every year from supporters across the United States on supporting Sinn Fein in Ireland.
This is because of electoral laws on both sides of the Border, which limit or preclude foreign donations.
Documents show that the group had a surplus of over $750,000. It raised more than $2.5m (€1.85m), but spent just $1.8m (€1.3m) over the past five years.
Last year, Friends of Sinn Fein paid for a 45-minute helicopter trip for Mr Adams, so that he could deliver a speech at the opening of a university museum on Ireland's Famine.
The group's biggest annual moneyspinner is the $500-a-head dinner (€370) hosted by Mr Adams at the luxury Sheraton Hotel in Manhattan.
Friends of Sinn Fein is required to reveal its donations to the US Department of Justice. Individuals, companies and a number of trade unions bankroll the group.
Friends of Sinn Fein previously used to send surplus funding to the North, with around $650,000 (€485,000) provided in the 12 months to the end of October 2007.
Under British electoral law, parties in the North can accept overseas donations, but only as long as they come from Irish or British citizens living abroad. Under Irish electoral law, Sinn Fein is not allowed to accept any foreign donations.
A lot of Friends of Sinn Fein's money is spent on paying for travel and accommodation for trips to the US by leading members of Sinn Fein, where they meet politicians, business leaders and activists.
The biggest sum is spent on catering – more than $500,000 in five years, including $128,000 (€95,000) in the six months to the end of last April.
A large chunk of the catering budget is spent on hiring the Imperial Ballroom in the Sheraton Hotel in midtown Manhattan for the annual Friends of Sinn Fein dinner hosted by Mr Adams every November.