DEAR DR. DONOHUE: I have had psoriasis for many years and have tried many medicines, but none has kept it under control. I am at my wits’ end and don’t know where to turn. Have you anything encouraging to offer? – B.M.

ANSWER: I can show you where to turn: to the National Psoriasis Foundation, whose number is 1-800-723-9166 and whose Web site is www.psoriasis.org. The foundation extends a helping hand to all psoriasis patients, fields their questions and provides them with the latest information on treatment.

Psoriasis is a skin condition that affects more than 5 million North Americans. The maturation of skin cells has gone out of control. Infant skin cells from the lower layers of the skin make a mad dash to the skin surface. The immature cells on the surface form raw, red patches covered with silvery scales.

Evidence mounts to implicate the immune system in this process. T cells, agents of the immune system, release products that waylay normal skin cell development. One of those products is tumor necrosis factor, or TNF.

I mention this only because there are now drugs that can block the pernicious influence of TNF on skin cells and hold out hope for those psoriasis patients who do not respond to standard psoriasis treatment. The names of these medicines are Remicade, Enbrel, Humira, Amevive and Raptiva. Some have yet to receive the official approval of the Food and Drug Administration for psoriasis (they are used for other illnesses), but all can be tried for patients with resistant psoriasis.

These medicines have two drawbacks. One is they must be injected. The second is they are expensive. It is important, therefore, for psoriasis patients to inquire of their insurers whether treatment with these agents is acceptable.

DEAR DR. DONOHUE: Every time I get my prescriptions filled, my pharmacist asks if I would like a generic substitute. Every time I say no. I don’t trust generics. I don’t want a cheap imitation of the real medicine. What is your opinion on generics? – B.N.

ANSWER: I use them on every occasion I can.

Generics are not cheap imitations of the real drug. They are the real drug. They must contain the same amount of active drug as the brand-name variety. They can contain different flavoring agents, preservatives and fillers than the brand name, but the differences end there. (Fillers are inactive ingredients.)

Drug companies hold a patent on a drug they have developed for 17 years. While the patent is in effect, the company markets the drug under a brand name of its choice, and the drug cannot be replicated by another company. The drug doesn’t really have 17 years of protection. During that time, the originating company has to test the drug’s safety and efficacy, so some years of protection are eaten up long before the medicine hits the market.

You don’t have to fear the potency of a generic drug. Almost all generics have as good a track record as the brand name.

If the doctor does not want the patient to have a generic substitute, the doctor can indicate that on the prescription by writing “DAW” – dispense as written.

You ought to reconsider your position. You are spending more money than you need to.

DEAR DR. DONOHUE: Some years back I had hepatitis B. I don’t know if I still have it. Two years ago I developed type 2 diabetes, and I take oral medicines for it. Could the hepatitis have caused me to get diabetes? – C.R.

ANSWER: Hepatitis (A, B or C) does not usually cause diabetes.

Type 2 diabetes comes from the body’s sluggish response to insulin. Insulin cannot push sugar into cells as it should. The result is a rise in blood sugar.

As an aside, you should find out if you still have ongoing hepatitis. Your doctor can run tests for liver enzymes to see if the virus is still around and still attacking liver cells. There are treatments for it.

DEAR DR. DONOHUE: I have had three clots in my leg veins. My doctor sent me to a blood specialist, who discovered I have factor V Leiden. He put me on blood thinners and said I will have to take them for life. I would appreciate any information on this condition. – R.W.

ANSWER: I simplify the process of blood clotting by talking only about blood platelets, the tiny blood cells that initiate a clot. However, the process is much more complicated, and it involves blood proteins, the so-called clotting factors.

Factor V (V for the Roman numeral 5) is one of those factors. Some people have a gene that has undergone a mutation and is responsible for a variant of factor V that promotes clots. One gene puts a person at seven times’ greater risk of having a clot than the rest of the population. Having two genes puts a person’s risk at 80 times that of the general population. Up to 7 percent of the white population has factor V Leiden, and that amounts to a large number of people.

When people with the factor V Leiden gene have had two or more clots, doctors usually put them on long-term blood thinners. Not only does this stop clot formation in veins, but it also prevents clot fragments from being swept in the circulation to the lungs. There they are called a pulmonary embolus and can be fatal.

“Leiden” comes from Leiden Hospital in the Netherlands, where this condition was discovered.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475.