Hey Jude, don't make it bad
Take a sad song and make it better
Paul McCartney explained that he wrote these lines in the hopes of cheering up John Lennon's son Julian, after John left Julian's mother Cynthia for Yoko Ono.
According to Julian, as a child, he was closer to McCartney than he was to his father.
After John Lennon left his first wife Cynthia in 1968, he and his five-year old son saw little of one another for almost two years. At the urging of a new girlfriend, May Pang (she came along during a period when John and Yoko were separated), Lennon renewed his relationship with his son in 1970.
But the tensions between Julian and his father were never fully resolved. As a young adult, Julian voiced bitterness toward his father and added that even as a very young child, he spent more time with Lennon's songwriting partner McCartney than with Lennon.
Julian once said, "Dad could talk about peace and love out loud to the world, but he could never show it to the people who supposedly meant most to him—his first wife, that is my mother Cynthia, and her son, me." (Source)
Julian blamed the estrangement partially on Yoko Ono. In a 1999 interview, he characterized her as "very manipulative" and described the frustration of being excluded by Ono from Lennon's will and then being forced to purchase some of his father's memorabilia at auction.
Despite the claims of neglect, Julian did receive musical encouragement from his father. John gave Julian a guitar and drum kit, and he also asked Julian to perform on his 1974 album Walls and Bridges.
Julian Lennon launched his own musical career in 1984 with Valotte. The album was nominated for a Grammy and two of its tracks, "Valotte" and "Too Late for Goodbyes," were released as singles and reached the top ten. Another single released two years later, "Stick Around," reached #1 on the American charts, but Lennon hasn't matched this success in the decades since.
Remember to let her into your heart
Then you can start to make it better
The minute you let her under your skin
Then you begin to make it better
These lines are the most frequently cited in the argument that "Hey Jude" is about heroin use.
These lines, coupled with the fact that "Judas" is common slang for heroin, have led many to argue "Hey Jude" is about using smack.
The argument's strained, and neither McCartney nor Lennon ever said anything to endorse the interpretation. In fact, all of their comments on the origins and meaning of the song implicitly deny that the song contains any sort of intentional reference to drugs.
Both Lennon and McCartney did, on the other hand, acknowledge their own drug use, as well as their reference to drugs in other songs. McCartney has said that the word "high" was usually used to suggest a drug-induced state.
McCartney acknowledged his use of cocaine and LSD, but his primary drug of choice was marijuana. In 1967, he went on the record in support of its legalization. He was also arrested four times for possession.
The most significant incident occurred in 1980, while he was touring Japan with the band Wings. The almost eight ounces discovered by customs officers in his luggage could have gotten him drug-trafficking charges. Instead, he was deported and told not to return.
That's probably a situation where being an internationally-beloved star works in your favor.