There is no excuse really when we have access to the internet and a quick google can tell everything about what drug one is prescribed and about to take (or not take).
checking google for tryptomine no where clearly suggests that its a sleep drug, let alone "dont drive while taking".
-Truth
Even with that said, if it did knock him out, it's slightly worrying that either he didn't read about the side-effects or there was no indication that this is a possible side-effect.
The amino acid tryptophan is available as an over-the-counter supplement in the US. It's often popularly blamed for post-Thanksgiving-dinner drowsiness, as it naturally occurs in turkey meat, but I recall seeing a debunking that the levels there are probably meaningless compared to other tiring rituals/portions of that traditional dinner.
In the US, prescriptions come with a long insert with tiny print with tons of drug information, and usually a smaller single-page larger-print insert mentioning the key dosage, side-effect, and counter-indications/incompatibility considerations.
It's also common for the prescribing doctor, and the separate pharmacist who usually 'fills' prescriptions, to add oral warnings about major considerations. These quite commonly include a "don't drive after taking" clause, or something to the effect of: "this makes many people drowsy, get used to its effects for a few days before doing anything risky".
Your point is well taken -- anyone given a new drug should learn as much about it as practical before taking it, from the person delivering it and other independent sources in print or via the web.
When rats were fed a diet completely lacking tryptophan for a short period, or a diet containing only one fourth of the “normal” amount for a more prolonged period, the results were surprising: They kept the ability to reproduce up to the age of 36 months (versus 17 months for the rats on the usual diet), and both their average longevity and their maximum longevity increased significantly. They looked and acted like younger rats. (A methionine-poor diet also has dramatic longevity-increasing effects.)
It has nothing to do with your post but I found it interesting.