Final years
Harry J. Anslinger criticized but supplied McCarthy's morphine addiction.

After his condemnation and censure, McCarthy continued to perform his senatorial duties for another two and a half years. His career as a major public figure, however, had been ruined. His colleagues in the Senate avoided him; his speeches on the Senate floor were delivered to a near-empty chamber or received with intentional and conspicuous displays of inattention.[165]

The press that had once recorded his every public statement now ignored him, and outside speaking engagements dwindled almost to nothing. Eisenhower, finally freed of McCarthy's political intimidation, quipped to his Cabinet that McCarthyism was now "McCarthywasm".[166]

Still, McCarthy continued to rail against communism and socialism. He warned against attendance at summit conferences with "the Reds", saying that "you cannot offer friendship to tyrants and murderers ... without advancing the cause of tyranny and murder."[167]

He declared that "co-existence with Communists is neither possible nor honorable nor desirable. Our long-term objective must be the eradication of Communism from the face of the earth." In one of his final acts in the Senate, McCarthy opposed President Eisenhower's nomination to the Supreme Court of William J. Brennan, after reading a speech Brennan had given shortly beforehand in which he characterized McCarthy's anti-Communist investigations as "witch hunts". McCarthy's opposition failed to gain any traction, however, and he was the only senator to vote against Brennan's confirmation.[168]

McCarthy's biographers agree that he was a changed man, for the worse, after the censure; declining both physically and emotionally, he became a "pale ghost of his former self", in the words of Fred J. Cook.[169]

It was reported that McCarthy suffered from cirrhosis of the liver and was frequently hospitalized for alcohol abuse. Numerous eyewitnesses, including Senate aide George Reedy and journalist Tom Wicker, reported finding him drunk in the Senate.

Journalist Richard Rovere (1959) wrote:

He had always been a heavy drinker, and there were times in those seasons of discontent when he drank more than ever. But he was not always drunk. He went on the wagon (for him this meant beer instead of whiskey) for days and weeks at a time. The difficulty toward the end was that he couldn't hold the stuff. He went to pieces on his second or third drink, and he did not snap back quickly.[170]

McCarthy had also become addicted to morphine. Harry J. Anslinger, head of the Federal Bureau of Narcotics, became aware of McCarthy's addiction in the 1950s, and demanded he stop using the drug. McCarthy refused.[171] In Anslinger's memoir, The Murderers (1961), McCarthy is anonymously quoted as saying:

I wouldn't try to do anything about it, Commissioner ... It will be the worse for you ... and if it winds up in a public scandal and that should hurt this country, I wouldn't care [...] The choice is yours.[171]

Anslinger decided to give McCarthy access to morphine in secret from a pharmacy in Washington, D.C. The morphine was paid for by the Federal Bureau of Narcotics, right up to McCarthy's death. Anslinger never publicly named McCarthy, and he threatened with prison a journalist who had uncovered the story.[171] However, McCarthy's identity was known to Anslinger's agents, and journalist Maxine Cheshire confirmed his identity with Will Oursler, co-author of The Murderers, in 1978.[171][172]