The distinction worth making early is between a tolerability problem, which is unpleasant and self-limiting, and a clinical problem, which is neither. They present differently and the thresholds for each are worth writing down before you need them.
Vomiting matters mostly through its consequences. Loss of gastric fluid depletes sodium, chloride and potassium, and hypokalaemia presents as exactly the fatigue and cramping people attribute to the drug. Persistent vomiting also makes a renal panel uninterpretable, because a pre-renal picture looks like renal impairment.
Gastrointestinal adverse events, indicative pooled rates
| Event | Active arm | Placebo arm | Timing |
|---|
| Nausea | 40–45 % | 15–20 % | Peaks 1–2 wk after each step |
| Vomiting | 15–25 % | 5–8 % | Follows nausea |
| Diarrhoea | 20–30 % | 10–15 % | Early, variable |
| Constipation | 20–25 % | 8–12 % | Later onset, persistent |
| Discontinuation for GI events | 4–7 % | 1–2 % | Mostly during escalation |
Ranges span agents and doses; read the specific prescribing information for a specific figure.
Concretely, distinguishing an injection-site nodule from an infection: a nodule is firm, non-tender or mildly tender, not warm, not expanding, and appears within a day or two. Cellulitis is warm, tender, expanding, and often accompanied by systemic features. A sterile abscess sits between the two and is fluctuant. Warmth plus expansion plus fever is the combination that stops being a forum question.
I would flag that attributing a symptom to a drug is a hypothesis, and the base rate of these symptoms in the general population is high enough that the hypothesis is often wrong.
Most of this resolves. The point of knowing the pattern is to recognise the small fraction that does not.