You're recreationally drinking medicine mixed with alcohol -- what do you expect? You wouldn't drink gin and asprin.

The article casually mentions "Quinine, used for hundreds of years to treat malaria, is a well known cause of platelet and bleeding problems..." The G&T was specifically mixed so colonial British could get their malaria medicine.

Ironically the origin of most cocktails was mixing in juices etc to cover up the taste of alcohol (even the romans had to water down their wine to make it palatable). But the G&T was mixing the alcohol in to make the medicine more palatable!