Horehound is most widely known for its expectorant properties which make it a good remedy for coughs, colds, and congestion. These expectorant properties also help to create a more effective cough because it loosens phlegm and helps to sooth tissues that can allow the phlegm to be ejected with ease.  
Health benefits include:
Is thought to be a good treatment for diabetes as it appears to lower blood sugar.
It is often used as a pain remedy. It can greatly reduce pain from toothaches, muscle cramps, sprains, and headaches.
Great for gallbladder health as it helps to stimulate the production of bile. 
It is a wonderful antispasmodic and can be used to treat nausea, vomiting, carsickness, and other stomach ailments.
It is great to take after a meal to help with digestion. It helps to decrease flatulence and bloating.
Cautions and Side Effects of Horehound
Do not use during pregnancy or while breastfeeding.
Children should not eat the seeds as it can cause poisoning.
Do not use for long periods of time as it can cause high blood pressure. Use when needed and not on a regular basis.