Lemon juice is more acidic than orange juice and more popular than lime juice. The acid helps to cut through the phlegm in the throat and make it easier to clear out. Honey, taken straight, is as effective at stopping coughs as any OTC cough syrup. It coats the back of the throat and soothes the irritated nerve endings. Unfortunately, the effect only lasts about 20 minutes. So, if you have an acute attack of coughing, it's great. If you've got a constant cough caused by a viral infection, you need something longer lasting.

Honey does not have a lot of microbes. Honey's properties kill microbes and fungi. Unpasteurized honey may have microbial spores - bacteria with a kind of protective shell. The worst of them is botulinum, the stuff that causes botulism poisoning. A healthy adult can eat unpasteurized honey with no ill effects, but children under one year of age and adults with weakened immune systems should never eat unpasteurized honey.

Opiates reduce the respiration reflex. For the doses found in cough syrup, it just means that it suppresses your coughing, but if you take too much of it, you will eventually stop breathing.

Due to the opioid abuse epidemic, doctors have pretty much stopped prescribing opioid-based cough suppressants unless the other stuff doesn't work. You'll get the other stuff that works up to a point but won't make you barf or get you high.