Ingredients do the same thing no matter if its a potion or a poison, you have to change the solvent for it to be a potion versus poison. This is just how ingredients work, but it could be beneficial to have drinkable poison for RP, getting out of combat, etc.
PC/NA Dungeoneer (Tank/DPS/Heal), Trialist (DPS/Tank/Heal), and amateur Battlegrounder (DPS) with a passion for The Elder Scrolls lore
CP 2000+
Warden Healer - Arcanist Healer - Warden Brittleden - Stamarc - Sorc Tank - Necro Tank - Templar Tank - Arcanist Tank
The various reagents (Beetle Scuttle, Blessed Thistle, Blue Entoloma, Bugloss, etc.) all have positive and negative effects. If you mix together ones with overlapping positive effects, you get helpful potions. If you mix together ones with overlapping negative effects, you get harmful potions. Kind of like how mixing together hydrogen and oxygen gets you something helpful like water, but mixing together hydrogen and chlorine gets you something much nastier. You wouldn't want to use hydrogen chloride on yourself, but to completely prevent hydrogen chloride from being possible, you would have to get rid of hydrogen and chlorine and there goes water and table salt!
So you have to think of the potion results arising from the reagents, rather than the resulting potions being an end unto themselves.
These are just alternative recipes for daily writs and for unlocking alchemy traits. I levelled up an alt today and used my excess water bottles instead of poison bottles whilst learning all the traits.