Treat a cold, the saying goes, and it will last for seven days. Leave it alone, and it will linger for a week.

Although the remedies don't cure the cold, sufferers still spend more than $1 billion annually for the relief and temporary comfort that over-the-counter drugs provide. Yet some of these medications can cause serious side effects.

Following are some of the drugs used to treat colds, and their side effects, according to Dr. William Jordan of the National Institute of Allergy and Infectious Diseases:

* Chlorpheniramine, an antihistamine used to shrink nasal membranes and decrease nasal secretion. Side effects include dizziness, drowsiness and bone marrow dysfunction. Some of the nonprescription drugs containing this ingredient are Contac, Chlor-Trimeton decongestant tablets, Coricidin tablets, Allerest and Dristan Ultra Colds Formula.

* Dextromethorphan, used for cough supression. Side effects include dizziness and upset stomach. Over-the-counter drugs with dextromethorphan include: Contac Severe Cold Formula capsules, CoTylenol Cold Formula capsules and tablets.

* Phenylpropanolamine, a nasal decongenstant that dries and shrinks nasal membranes. Side effects include nervousness, insomnia, increased blood pressure and heart rate. Among the drugs that contain this ingredient are: Triaminicin tablets, Contac and Allerest.

* Pseudoephedrine, a nasal decongestant. Side effects include increased blood pressure and heart rate. Drugs that contain this ingredient include: Chlor-Trimetron Decongestant Repetab tablets, Contac Severe Cold Formula, DayCare Daytime Colds Medicine, Dristan Ultra Colds Formula and CoTylenol tablets.

Some treatments, such as the age-old "plenty of rest," have no side effects. There's also some scientific evidence that Grandmother's prescription for vaporizers and chicken soup was on the mark. It seems that hot steam warms tender nasal passages and kills some of the cold viruses.

One of the newest treatments for colds works on this principle. Known as Rhinotherm, the machine delivers a controlled dose of steam through a special nozzle that fits under the nose. Rhinotherm has Food and Drug Administration approval for symptomatic relief of colds and allergies and is marketed by Ascot Pharmaceuticals. It has one drawback: a $500 price tag.

As for vitamin C, the controversy rages. The latest findings suggest that vitamin C is ineffective in combating colds, a finding disputed by vitamin C proponent Linus Pauling.

Also not yet proven are zinc gluconate lozenges. One clinical study found the lozenges effective in treating colds, but that work has yet to be reproduced by other laboratories, and the tablets are not approved by the FDA for use against colds.

Soon to be on the market is Avert, a facial tissue developed by Kimberly Clark and now being test marketed in upstate New York. At the Interscience Conference on Antimicrobial Agents and Chemotherapy meeting last fall, University of Wisconsin virologist Elliott Dick reported that Avert limits cold contagion by killing viruses shed from the nose. The three-ply tissue is treated with an acid that is harmful to cold viruses but not to the nose.

Since the tissue does nothing for the cold sufferer, its use -- at about twice the cost of regular tissue -- is an act of altruism. But it could be helpful to families who want to cut infection rates among members.

Unlike cold sufferers, flu victims have a few more options when it comes to treatment and prevention. Vaccines protect against many types of flu. There's also the drug Amantidine, which is effective in treating influenza if it is given during the first two days of the infection. Despite its effectiveness, Amantidine has not yet caught on in the medical community, reports Dr. Jack Gwaltney of the University of Virginia's School of Medicine.

Two other antiviral drugs are in clinical trials. One is Rimantidine, a sister drug to Amantidine. The other is Ribavirin. Administered by aerosal, Ribavirin seems to be effective in treating influenza A and B. It works by stopping virus reproduction long enough for the immune system to fight back.

There's hope that Ribavirin might also be effective against some cold viruses. Studies show that Ribavirin can't offer relief against rhinovirus, according to Dr. Vernon Knight, who is testing the drug at Baylor University. But the results of some preliminary work suggests that it may be effective against RSV, the cold virus that can be so harmful to infants.