You probably read this on Wikipedia or another article on the internet.
It turns out not to be true. According to a news article from 1972 George Sanders checked into the hotel two days ago, but died the same night after taking Nembutal. He probably also took a low dose of Nembutal, as the bottles in the 1970s contained between 0.5 and 1.5 grams of pentobarbital per bottle.
This news article from 1972 shows George Sanders had gone to bed at 9pm on monday and asked to be awakened early because he planned to fly to Nice. He was found dead in the morning.
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