There is no 'maximum dose' of oestrogen. We prescribe in accordance with international best practice, starting on a small dose and gradually increasing it based on your bloodwork until you reach the optimum level.
For instance, with oestrogen pills (oestradiol valerate) we would typically begin around 1-2mg daily, but our protocols do not exceed a maximum dosage of 8mg daily. Dosages in excess of 8mg would need to be signed off by our medical team in each case, although it is highly unlikely that this will be required.
Excessive oestrogen can both cause health risks and have a counter-productive effect on the transition process. To ensure that you have the safest and smoothest transition, you should always take the prescribed dosage.