How to Know What to Take for a Cold : Health: The choices of remedies are plenty. Here’s a no-nonsense explanation about some of them.

Feeling lousy and fuzzy-headed from a cold?

Well, trying to sort out the remedies on drugstore shelves could leave you feeling even worse. Manufacturers--aiming for a share of the more than $2-billion-a-year over-the-counter cold, allergy and sinus remedy market--throw a head-spinning array of products at consumers.

Here’s what you are faced with:

Antihistamines

* Common drugs: Chlorpheniramine maleate, Diphenhydramine, Promethazine, Terfenadine, Triprolidine.

* What they do: Designed to counter the effects of histamine, the chemical produced by the body in an allergic reaction to dust, pollen and other allergies. It is histamine that causes the sneezing, red eyes and runny nose of an allergy.

Antihistamines vary in their effectiveness. Diphenhydramine, for example, is good for itching or a bee sting but less effective for nasal problems. Chlorpheniramine is more effective for those.

* Side effects: Over-the-counter antihistamines cause drowsiness. Some also may cause loss of appetite, nausea, dry mouth, blurred vision and difficulty urinating.

Decongestants

Common drugs: Ephedrin, Oxymetazoline, Phenylpropanolamine, Pseudoephedrine.

* What they do: Decongestants help ease a stuffy nose by constricting blood vessels, which reduces inflammation in the nasal passageways. In addition, they help prevent a buildup of mucus that might lead to sinus infection.

* Side effects: Decongestants generally keep people awake. Also, because they can lead to tremors, these drugs are generally not recommended for people with heart disease, high blood pressure, thyroid disease or diabetes. They can also be harmful to some patients who are taking medication for depression.

Harmful side effects are lessened when decongestants are used as nasal drops because only small amounts of the drugs are absorbed into the bloodstream. However, overuse of nasal sprays can lead to even greater congestion--called rebound congestion--when the sprays are discontinued.

Pain Relievers

* Common drugs: Aspirin, Acetaminophen and Ibuprofen.

* What they do: These drugs, which can be easily purchased by themselves, are also frequently added to cold and allergy medications. They reduce pain and fever to help the patient feel more comfortable.

* Side effects: If a fever is present and the patient has the flu, aspirin can cause Reye’s syndrome in children, a rare disease that can kill or disable. Aspirin can also produce stomach problems.

Cough Relief

* Common drugs: Ammonium chloride, Codeine, Dextromethorphan, Guaifenesin.

* What they do: There are two types of over-the-counter cough-relief medications. Expectorants, such as ammonium chloride and guaifenesin, are designed for coughs that are producing phlegm. They increase the secretions in the lung to make the phlegm looser. Some expectorants also help make the phlegm less sticky.

The other cough medications are suppressants, such as codeine and dextromethorphan. They act on the brain to control the coughing reflex.

* Side effects: Cough medications can cause drowsiness. Overdosing can sometimes slow breathing.

Sources: American Medical Assn. Encyclopedia of Medicine, Public Citizen Health Research Group, Dr. Allan M. Weinstein.