Side effects from GLP medications vary hugely from person to person, a dose that will make one person throw up for a week might not be noticeable to someone else, but usually once the doses get a bit higher it becomes more obvious. Even different GLP's can have unexpectedly different effects, I had horrible nausea even on tiny doses of ozempic at 0.2mg/2nd day, but next to nothing from 4.5mg of tirz/2 days. The fact that there was some appetite suppression is good evidence the GLP is OK,( not sure if reta or tirz.) and not fake. Not from the research, just from reading this forum, people who are less overweight often seem to have effects and side effects at lower doses than people who are severely overweight. The other thing to know is due to the long half life of 6-7 days, side effects that are unpleasant can last a long time, they are usually worst the day or 2 after a dose, but can last a week or more, which becomes a major problem if those effects are diarrhoea or vomiting as it can cause dehydration, which is the main way to get very unwell and need a hospital visit from taking GLPs.
In general if you have zero side effects at a given dose , bumping up a bit like from 3mg to 4mg is unlikely to cause severe side effects, but nothing is impossible. It is always worth checking out GLP plotter to see what drug levels do over time, it helps to make sense of the effects and side effects over time, as a given dose will only peak in level after the 4th weekly dose. The other method for pushing up doses with lowest risk of side effects is to just have an extra mg halfway between usual doses . As side effects relate to dose peaks, you are much less likely to have adverse effects with smaller more frequent doses than single larger ones, but you need to read up on the pharmacokinetics and understand it by using GLP plotter if you want to mess with dosing intervals.