"It looks like a doctor's handwriting" is universal for "It's illegible." But the handwriting of physicians isn't much worse than others.' Or how could pharmacists read it?

The problem is that prescriptions are written in symbols not understood by most patients, and the drug names are unfamiliar. Actually, prescriptions are fairly easy to read these days -- phsicians are no longer schooled in Latin.

There are several advantages to being able to read your own prescription. The most important is to facilitate a dialogue between you and your physician so that you understand the directions and know what the drug should do for you, what side effects to expect, and whether and when you should refill it.

Instead of taking the prescription from the doctor and leaving, you can say something like, "Doctor, I see that you want me to take two doses of drug X three times a day. At what time would it be best to take them? Are there any foods or drinks I should avoid?"

Or, "I think, doctor, that you gave me this drug Y once before -- do I have the name right? -- and it made me very nauseous." Or, "I think we have some of this drug Z left from Henry's bout with gout. Does it keep, and can I take Henry's pills rather than get this prescription filled?"

Another advantage of reading your prescrition: You can see if the drug name and directions on the pharmacist's container match those the doctor wrote on the prescription. Also, if you know the name, strength, and number of dosage units on the prescription, you can comparison-shop for the best price, and check to see if you received as many pills as prescribed.

There are two main parts to the prescription: 1) the drug name, strength and number of dosage units (tablets, capsules, or milliliters); and 2) directions for use -- usually the most mysterious part. The "Rx" printed on the prescription blank stands for "take thou."

The drug name is sometimes in the generic form, but is usually a manufacturer's trademarked brand name. If the manufacturer's patent has not expired, that company is usually the only one making it, so it doesn't matter whether the brand or generic name is on the prescription. If the patent has expired, many companies may be competing for sales of the same generic product under different brand names. In the latter case, it is often much better (potentially cheaper) to have your drug requested by generic name.

Before he or she writes your prescription, you may ask your physician to use the generic name. Or you may ask the pharmacist to dispense the generic product if he has it.

After the drug name is the drug strength, most often in milligrams (mg), milligrams per milliliter (mg/ml) in the case of liquids, and for some drugs, units. For example, diazepan (valium) comes in 2-, 5-, and 10-mg tablet sizes. A liquid antibiotic such as ampicillin can be 100 mg per ml, or 125 mg, 250 mg, or 500 mg per 5 ml (per teaspoon). Birth-control pills may be in micrograms (mcg); insulin is always in units, and penicillin is sometimes in units. (A unit simply means a standard amount.)

After the drug name and strength is the number of dosage units. Examples are #30, or Roman numerals XXX, for tablets and capsules, and 15 ml, 150cc, or 1 pt for liquids.

Rarely are the more mysterious apothecary measures used these days. Exceptions are aspirin, thyroid, phenobarbital, and nitroglycerin, all common drugs often sold in grains (gr). There are about 60 mg in 1 gr so that a 5-gr tablet represents about 300 mg. Sometimes the physician writes the number of dosage units ordered in Roman numerals because it is believed the patient would have more of a problem trying to alter the number ordered on the prescription.

Directions known as the Sig (for the Latin word Signatura ) are the most difficult for people to read because they are a combination of convention and shortcut Latin. Physicians often don't know the Latin words for the symbols they're using, but they've learned the meanings.

Some common symbols used in prescription writing: prn: take when needed ud: as directed ut dict: as directed qam: every morning qd: every day bid: twice a day tid: three times a day qid: four times a day qod: every other day q4h, q6h: every 4 hours, every 6 hours stat: at once, immeditately hs: at bedtime pc: after meals ac: before meals po: by mouth gtts: drops os: left eye od: right eye c: with s: without

The number of dosage units to be taken each time is customarily given in lower-case Roman numerals. Thus i,ii, iii and iv respectively denote one, two, three and four -- and ss means one-half. Knowing the terminology, it is easy to translate directions such as: "tabs iss tid 1 hr ac, hs po" ("Take 1 1/2 tablets three times a day one hour before meals and at bedtime by mouth.") Or, "caps 1 prn ud" ("Take one capsule as directed when needed.")

Prescription forms usually have an "R," "Ref." or "Rep.," followed by a line for the physician to write the number of refills allowed. Or there may be a series of numbers, one of which may be circled. Or the physician may simply write "R" and the number of refills allowed.

If the "No" box is checked next to "Label as to Contents," that means the doctor does not want the pharmacist to type the name of the drug on the label (which means you are not intended to know the drug's name). You may want to inquire about the reason.

The prescriber may also indicate that he or she does not wish the pharmacist to substitute a generic equivalent, but to dispense the brand name written. The procedure varies in the District, Maryland and Virginia. All three jurisdictions, however, have passed legislation permitting the pharmacist to automatically substitute equivalent medications, even if prescribed by brand name unless the prescriber indicates otherwise.

In Virginia the physician signs on one of two lines stating either "Voluntary Formulary Permitted" or "Dispense As Written." In Maryland, which has no specific procedures, the prescriber may indicate "Brand Name Only" or "Dispense As Written" or "DAW." In D.C., the physician designates "Dispense As Written" or "DAW" in his or her own handwriting.

By law, the prescription must be signed by a licensed physician, osteopath, dentist, or veterinarian. If the prescription is for a controlled substance, the prescription must also carry the prescriber's DEA (Drug Enforcement Administration) registration number.

Not all prescription forms are identical, but they're similar enough so that armed with this knowledge, your should be able to translate any prescription, look your doctor in the eye and say, "Now doctor, about this prescription . . ."