i interpreted this in 2 ways: one in a literal way which is about drugs, one in a metaphoric way which is about sex.

“Then she fell in love with a pill that could take away all her pain, yuh / Then she fell in love with a whole new drug that could fill her veins / She's high / She lives in the sky / Tonight, she's satisfied / Rolling back her eyes / But then, she starts to cry / Everything is turning to black / All in one night / She just went to heaven and back”

as we know, the pills as drugs ‘can take away all her pain’, meaning that these drugs gives her an ecstatic feeling after consuming it. in result, she ‘fell in love’ with it and became addicted and ‘high’. afterwards, it describes the effects after taking the pills.

on the other side. if we think that the ‘pill’ refers to a dick (because of the shape), the meaning of what i just explained changes completely. she gets satisfied, she rolls her eyes, she may end up tearing up due to the pleasure, and these behaviors can also be found when taking drugs. when we think of sex or when we have it, most of the times it has the addicting feeling like taking a drug, a pill, which leaves us having that ecstatic feeling