I remember having learned it from the TV. But I can't remember what it is now. It's a verb synonym of drug or poison. It means someone slips some drug into someone's food or water. The drug may be just some sedatives.
I think in relation to alcohol, you may be thinking of "Slip a Mickey" or "Mick" or "Roofie".
to add a small amount of a powerful substance (such as alcohol, a drug, or a poison) to (something, such as a drink)
That would possibly be "spiking" (i.e., spiking someone's drink). Hope this helps!
If the drug being slipped is a psychedelic like LSD, the word dose is often used.
Example from SF Weekly
It's been over 50 years, but Wayne Ritchie says he can still remember how it felt to be dosed with acid.
He was drinking bourbon and soda with other federal officers at a holiday party in 1957 at the U.S. Post Office Building on Seventh and Mission streets. They were cracking jokes and swapping stories when, suddenly, the room began to spin. The red and green lights on the Christmas tree in the corner spiraled wildly. Ritchie's body temperature rose. His gaze fixed on the dizzying colors around him.
Example from Time Magazine:
The article mentioned a narcotics officer he once knew and noted the officer’s involvement in the LSD experiments; then it hit Ritchie that he might have been secretly dosed on the day he went crazy.
Example from The Guardian:
On board were half a dozen travellers who called themselves the Merry Pranksters and a jar of orange juice laced with LSD.
After Cassady drove the bus off the road in Arizona, Kesey dosed the party with LSD.
For the skeptics, headlines using the word "dosed" to describe people being given drugs without knowing it:
High school teacher recounts being dosed (BoingBoing)
Security guard ‘dosed’ with GHB and LSD at B.C. music festival (Canada.com)
Worst Science Article of the Week: The CIA Dosed a French Town With LSD! (Discover Magazine)
R.I.P. "Oscar": Dog Dosed With LSD By Owners Dies After Being Struck By Car (The Smoking Gun)
The Plymouth Diaries: That Time A Neo-Nazi Dosed Me With LSD (Remy Carreiro)
Family Gets Dosed With LSD From Walmart Steaks (Bubblews)
The History of "What if We Dosed the Water?" (Brainsturbator)
Johnny Knoxville Was Dosed With Ecstasy While Filming 'Jackass Presents: Bad Grandpa' Promos (Huffington Post)
And here's a "confession bear" meme somebody made: