Any reinforcer that has the potential to affect the health of the client adversely if used inappropriately or in excess is called a:

Positive reinforcer

positive reinforcement can lead to adverse effects, and it is implicated in a range of personal and societal problems. If used inappropriately or in excess, it can change the health of a client negatively. 

Negative reinforcer

Explanation:

Reinforcement is the process which is used to strengthen the ability of a person to take a specific decision and the person involved in this process of reinforcement is known as a reinforcer.Some of the reinforcers are negative as they may affect the client's health adversely and may also hinder his development. Such reinforcers should be avoided.