Look at the placebo arm before concluding anything about attribution. The placebo-arm rates for most of these events are not small, because the events themselves are common in the underlying population.
Constipation outlasts the nausea because it has two causes and only one of them resolves. Gastric emptying accommodates over weeks; total intake, and therefore stool volume and the osmotic load reaching the colon, does not recover until intake does. This is why fibre alone can make it worse — you add bulk to a system that is short of water and short of motility.
Concretely, 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.
SURMOUNT-1 reported gastrointestinal events as the most frequent adverse events, mostly mild to moderate and mostly during escalation, with discontinuation for adverse events in the single digits per cent[1].
One qualification — reported incidence in a monitored trial population is a lower bound on what happens in an unmonitored one, because trial participants were escalated to protocol and supported through it.
If the timing does not fit the escalation, look for another explanation before settling on the drug.
edited 10 Dec 2024 by u100_marks — fixed an arithmetic slip in the third paragraph