Nyarlep:
I would be wary of taking any of the gen 1 antihistamines on a regular basis. There are both a bevy of known undesirable sideffects and some worrying studies into links to neural degenerative diseases and long term use of those kinds of meds. I doubt op is planning on taking it for years but do be careful.
I remember a few years ago, there were a bunch of women taking apetamin to gain weight. They were not feedists, mind you. They were mostly skinny women looking to gain some curves.
Most of them stopped due to a tank in quality of life.
Those first gen antihistimens are no joke. Sure, some of them are still used, but they are for short-term use under doctor supervision. For example, one of the potential side effects is low blood pressure.
Never mess with medication willy nilly. Even OTC meds need to be taken with caution.