Why do some drugs require you to take them in an "upright position"? A friend of mine was taking the supplement Metamucil and on the container it says to take in an "upright position." Why would this be necessary? Doesn't your digestive system push food/liquid downwards anyways?

Metamucil is taken as a drink. You're more likely to aspirate versus swallow when drinking supine if you're ill with impaired swallowing reflexes.

It's also recommended that you take bisphophonates standing up so that gravity, and a glass of water, make sure the drug passes into the stomach. It can be highly corrosive if it gets stuck in the esophagus.