I'm taking Cialis daily 5 mg with mild result. Can I boost adding ocassionally a 10mg on demand?

It is best to discuss this with your prescribing doctor.

This is the dosing guideline for Cialis.

CIALIS for Use as Needed

The recommended starting dose of CIALIS for use as needed in most patients is 10 mg, taken prior to anticipated sexual activity.

The dose may be increased to 20 mg or decreased to 5 mg, based on individual efficacy and tolerability. The maximum recommended dosing frequency is once per day in most patients.

CIALIS for use as needed was shown to improve erectile function compared to placebo up to 36 hours following dosing. Therefore, when advising patients on optimal use of CIALIS, this should be taken into consideration.

CIALIS for Once Daily Use

The recommended starting dose of CIALIS for once daily use is 2.5 mg, taken at approximately the same time every day, without regard to timing of sexual activity.

Expand this post...

The CIALIS dose for once daily use may be increased to 5 mg, based on individual efficacy and tolerability.

http://www.drugs.com/dosage/cialis.html