I am involved in a trial comparing the withdrawal patients staying in an in-patient unit experience after discontinuing either two drugs. The drug they were taking before are not randomised.

A reviewer of the ethics proposal enquired about whether we were following intention-to-treat principles.

I never even considered using intention to treat since:

(i) participants cannot switch drugs during treatment since they are only being measured after they have stopped (ii) participants were not randomised, the decision to use either drug was based on the preferences of the prescribing doctor and the participant.

But just say participants decide the withdrawal they experience is too intense and want to resume use of either the drug they were originally on or the other drug. If they agree to continue providing withdrawal symptom data should their withdrawal symptom data still be analysed as if they had never resumed use of the drug?

From what I understand from here and here intention to treat preserves the bias-removal effect inherent in randomisation.

But does intention to treat offer the same advantages when there is no randomisation?

As you can tell I am a bit confused and would welcome some clarity.