What is the point of Bad Medicine?
Solution 1:
It can be used as a damaging spell because it can be used to target enemies. You gain a total of 2 damage against them. It is best used on targets at the beginning of the battle as they do not gain any of the healing and take a total of 4 damage (credit Brysonic).
Alternatively, if you know that one of your party members is going to die, but has a really good card that you want them to use before they die, you can give them a 2HP boost for this round before they die next round.
Solution 2:
There is another potential use that this card has, that isn't mentioned in Sorean's answer.
In addition to between 2 and 4 points of total damage (depending on whether the enemy was at full health when it was cast), and the 2 points of healing at the time of cast, the card has a duration, and therefore adds a status effect card to your target. This is important because targets can only have a total of three status effect cards active at any one time. If a target already has three status effect cards, and a fourth is applied, the oldest one is pushed off and expires.
So potentially this card can be used in conjunction with other cards with durations to remove enemy buffs.
If you have 2-3 different cards with durations, such as Bad Medicine, Freeze, and Entangling Roots, you can unload them on an enemy and remove beneficial buffs they may already have, such as Mass Frenzy and Impenetrable Nimbus.
Cards like this can also be used to remove negative debuffs or traits from your own characters. Nasty traits like Superstitious, or spells like Mind Worm, might be worth the cost of dropping Bad Medicine and 2 other spells on your own character.