I've noticed that making a normal Damage Health potion at my level does around 33 points of health damage. Some ingredients however do more damage, even though there is no indication as to why that is so.

For example: using a Deathbell in a DH potion does 48 points of damage, while using a river betty does a whopping 81 points.

Way to spoil alchemical effects for me

It probably has to with the rareness of the ingredient, how difficult it is to find. The River Betty is a fish, and not just a plant, so I would think it would do more. So, if you use better or rare ingredients, along with fortify alchemy gear, you will get stronger (and more expensive) potions in the process. They will also become stronger as you level the skill.

Because most ingredients are better quality, like the Jaren root you get from Astrid, instead of using it for what it was for I made an extremely deadly potion.