The forum you are looking for is Deliriant Antihistamines
Please do not use SWIM, but avoid self-incrimination.
This is hardly a 'high'. One would do well to thoroughly research this area before trying to experiment with high doses of antihistamines. These are anticholinergic agents. The experiences are rarely enjoyable and the hallucinations produced can be difficult to distinguish from reality. I highly recommend the user find another way to 'get high'.
Additionally, cetrizine can be particularly dangerous for some people with any history of asthma or related breathing problems. If one is insistent on experimenting, then I highly recommend trying a low (or regular therapeutic) dose first to ensure the subject has no dangerous interactions.