The drugs that we take have a time of activity in our organism and for this reason they are indicated with an administration interval. It follows that one should be as strict as possible with all the medication, since forgetfulness could lead to a drop in the concentrations of the drug in the body, and therefore, the partial or total loss of its effectiveness.
It is not possible to determine the negative effect of forgetting a particular dose, since it depends on several factors such as the total dose administered, the dosing interval, the number of days we have been taking it, etc... However, I do not believe that missing a single progesterone tablet has any side effects.
When we have the feeling that this has happened we should restart taking it as soon as possible and even if we have doubts we can take a supplementary pill, since no side effects have been observed from increasing the administration of progesterone from 600 to 800 or 1000 mg per day (from 3 to 5 tablets of 200 mg).