There are two ways to identify effective groups of drugs. The first is to look at formularies or guidelines that exist in your hospital or health system, or at international guidelines, such as the WHO treatment guidelines for certain common disease groups, or the WHO Model List of Essential Drugs. Another way is to check the index of a good pharmacology reference book and determine which groups are listed for your diagnosis or therapeutic objective. In most cases you will find only 2-4 groups of drugs which are effective. In Annex 2 various sources of information on drugs and therapeutics are listed.
Exercise Look at a number of advertisements for new drugs.
You will be surprised at how very few of these 'new' drugs are real innovations and belong to a drug group that is not already known.