To be exact about it, the honest framing is that this is very common, usually self-limiting, and occasionally the presentation of something that is not self-limiting at all — and the differentiating features are specific enough to be worth knowing.
Nausea incidence in the pivotal trials runs to roughly 40 to 45 per cent at the higher doses against 15 to 20 per cent on placebo, with vomiting at roughly 15 to 25 per cent against 5 to 8 per cent. Discontinuation specifically attributable to gastrointestinal adverse events was in the range of 4 to 7 per cent. Those are the numbers to hold in mind when someone describes their experience as unusual.
Fatigue attribution is a subtraction problem. Take out the energy deficit, the dehydration, the electrolyte shortfall and the poor sleep, and what remains attributable to the drug in the trials was modest — placebo-arm fatigue rates were within a few points of active-arm rates in most of the programme. The corollary is that the fixable causes are usually the actual causes.
The prescribing information for each agent lists adverse reaction frequencies against placebo in a table, and reading that table is more informative than reading a hundred anecdotes, because it has a denominator.
The limitation of the timing heuristic is that it works well for common events and poorly for rare ones, which are precisely the ones that matter most.
If the timing does not fit the escalation, look for another explanation before settling on the drug.